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 $59.98   6.198%   $63.6976   $63.70   $63.70   $63.70  
  Purchase #2 $26.98   13.180%   $30.536   $30.54   $30.55   $30.50  
  Purchase #3 $202.80   13.160%   $229.4885   $229.49   $229.50   $229.50  
  Purchase #4 $60.32   11.188%   $67.0686   $67.07   $67.05   $67.10  
  Purchase #5 $141.43   5.787%   $149.6146   $149.61   $149.60   $149.60  
  Purchase #6 $97.75   8.676%   $106.2308   $106.23   $106.25   $106.20  
  Purchase #7 $217.88   4.399%   $227.4645   $227.46   $227.45   $227.50  
  7 purchase totals = $807.14       $874.1006   $874.10   $874.10   $874.10