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 $65.63   4.410%   $68.5243   $68.52   $68.50   $68.50  
  Purchase #2 $147.71   6.297%   $157.0113   $157.01   $157.00   $157.00  
  Purchase #3 $152.40   10.707%   $168.7175   $168.72   $168.70   $168.70  
  Purchase #4 $59.86   4.181%   $62.3627   $62.36   $62.35   $62.40  
  Purchase #5 $133.56   6.725%   $142.5419   $142.54   $142.55   $142.50  
  Purchase #6 $53.95   5.114%   $56.709   $56.71   $56.70   $56.70  
  Purchase #7 $125.47   9.132%   $136.9279   $136.93   $136.95   $136.90  
  7 purchase totals = $738.58       $792.7946   $792.79   $792.75   $792.70