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 $209.53   5.735%   $221.5465   $221.55   $221.55   $221.50  
  Purchase #2 $63.91   8.246%   $69.18   $69.18   $69.20   $69.20  
  Purchase #3 $65.73   4.286%   $68.5472   $68.55   $68.55   $68.50  
  Purchase #4 $65.46   8.779%   $71.2067   $71.21   $71.20   $71.20  
  Purchase #5 $97.58   7.336%   $104.7385   $104.74   $104.75   $104.70  
  Purchase #6 $206.63   8.831%   $224.8775   $224.88   $224.90   $224.90  
  Purchase #7 $41.72   9.650%   $45.746   $45.75   $45.75   $45.70  
  7 purchase totals = $750.56       $805.8424   $805.86   $805.90   $805.70