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 $210.40   11.523%   $234.6444   $234.64   $234.65   $234.60  
  Purchase #2 $21.89   3.782%   $22.7179   $22.72   $22.70   $22.70  
  Purchase #3 $241.94   6.217%   $256.9814   $256.98   $257.00   $257.00  
  Purchase #4 $240.76   8.812%   $261.9758   $261.98   $262.00   $262.00  
  Purchase #5 $125.30   3.445%   $129.6166   $129.62   $129.60   $129.60  
  Purchase #6 $64.43   6.355%   $68.5245   $68.52   $68.50   $68.50  
  Purchase #7 $222.29   6.324%   $236.3476   $236.35   $236.35   $236.30  
  7 purchase totals = $1,127.01       $1,210.8082   $1,210.81   $1,210.80   $1,210.70