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 $188.45   12.373%   $211.7669   $211.77   $211.75   $211.80  
  Purchase #2 $247.77   8.605%   $269.0906   $269.09   $269.10   $269.10  
  Purchase #3 $59.45   11.421%   $66.2398   $66.24   $66.25   $66.20  
  Purchase #4 $170.81   3.621%   $176.995   $177.00   $177.00   $177.00  
  Purchase #5 $119.99   9.531%   $131.4262   $131.43   $131.45   $131.40  
  Purchase #6 $177.47   9.817%   $194.8922   $194.89   $194.90   $194.90  
  Purchase #7 $218.51   7.608%   $235.1342   $235.13   $235.15   $235.10  
  7 purchase totals = $1,182.45       $1,285.5449   $1,285.55   $1,285.60   $1,285.50