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 $213.48   10.552%   $236.0064   $236.01   $236.00   $236.00  
  Purchase #2 $221.46   8.264%   $239.7615   $239.76   $239.75   $239.80  
  Purchase #3 $88.52   10.594%   $97.8978   $97.90   $97.90   $97.90  
  Purchase #4 $113.79   9.838%   $124.9847   $124.98   $125.00   $125.00  
  Purchase #5 $151.30   4.861%   $158.6547   $158.65   $158.65   $158.70  
  Purchase #6 $77.39   3.796%   $80.3277   $80.33   $80.35   $80.30  
  Purchase #7 $234.49   13.660%   $266.5213   $266.52   $266.50   $266.50  
  7 purchase totals = $1,100.43       $1,204.1541   $1,204.15   $1,204.15   $1,204.20