Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $177.71   13.650%   $201.9674   $201.97   $201.95   $202.00  
  Purchase #2 $113.90   11.190%   $126.6454   $126.65   $126.65   $126.60  
  Purchase #3 $111.91   9.580%   $122.631   $122.63   $122.65   $122.60  
  Purchase #4 $236.38   10.263%   $260.6397   $260.64   $260.65   $260.60  
  Purchase #5 $135.84   10.390%   $149.9538   $149.95   $149.95   $150.00  
  Purchase #6 $150.51   3.849%   $156.3031   $156.30   $156.30   $156.30  
  Purchase #7 $108.85   13.625%   $123.6808   $123.68   $123.70   $123.70  
  7 purchase totals = $1,035.10       $1,141.8212   $1,141.82   $1,141.85   $1,141.80