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 $65.89   4.500%   $68.8551   $68.86   $68.85   $68.90  
  Purchase #2 $123.97   6.766%   $132.3578   $132.36   $132.35   $132.40  
  Purchase #3 $105.41   13.477%   $119.6161   $119.62   $119.60   $119.60  
  Purchase #4 $59.79   11.188%   $66.4793   $66.48   $66.50   $66.50  
  Purchase #5 $122.86   4.669%   $128.5963   $128.60   $128.60   $128.60  
  Purchase #6 $69.47   13.603%   $78.92   $78.92   $78.90   $78.90  
  Purchase #7 $237.41   11.686%   $265.1537   $265.15   $265.15   $265.20  
  7 purchase totals = $784.80       $859.9783   $859.99   $859.95   $860.10