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 $212.98   10.797%   $235.9755   $235.98   $236.00   $236.00  
  Purchase #2 $173.44   8.804%   $188.7097   $188.71   $188.70   $188.70  
  Purchase #3 $143.30   8.373%   $155.2985   $155.30   $155.30   $155.30  
  Purchase #4 $95.82   6.873%   $102.4057   $102.41   $102.40   $102.40  
  Purchase #5 $224.46   12.315%   $252.1022   $252.10   $252.10   $252.10  
  Purchase #6 $101.91   4.732%   $106.7324   $106.73   $106.75   $106.70  
  Purchase #7 $215.80   4.759%   $226.0699   $226.07   $226.05   $226.10  
  7 purchase totals = $1,167.71       $1,267.2939   $1,267.30   $1,267.30   $1,267.30