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 $182.85   11.204%   $203.3365   $203.34   $203.35   $203.30  
  Purchase #2 $24.69   7.744%   $26.602   $26.60   $26.60   $26.60  
  Purchase #3 $59.31   5.303%   $62.4552   $62.46   $62.45   $62.50  
  Purchase #4 $94.43   11.464%   $105.2555   $105.26   $105.25   $105.30  
  Purchase #5 $61.41   7.468%   $65.9961   $66.00   $66.00   $66.00  
  Purchase #6 $116.26   11.630%   $129.781   $129.78   $129.80   $129.80  
  Purchase #7 $63.46   7.163%   $68.0056   $68.01   $68.00   $68.00  
  7 purchase totals = $602.41       $661.4319   $661.45   $661.45   $661.50