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 $228.65   3.437%   $236.5087   $236.51   $236.50   $236.50  
  Purchase #2 $98.68   8.584%   $107.1507   $107.15   $107.15   $107.20  
  Purchase #3 $123.55   9.846%   $135.7147   $135.71   $135.70   $135.70  
  Purchase #4 $212.97   11.734%   $237.9599   $237.96   $237.95   $238.00  
  Purchase #5 $225.30   4.473%   $235.3777   $235.38   $235.40   $235.40  
  Purchase #6 $97.93   10.289%   $108.006   $108.01   $108.00   $108.00  
  Purchase #7 $59.62   9.262%   $65.142   $65.14   $65.15   $65.10  
  7 purchase totals = $1,046.70       $1,125.8597   $1,125.86   $1,125.85   $1,125.90