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 $129.95   8.844%   $141.4428   $141.44   $141.45   $141.40  
  Purchase #2 $235.72   3.804%   $244.6868   $244.69   $244.70   $244.70  
  Purchase #3 $168.37   3.170%   $173.7073   $173.71   $173.70   $173.70  
  Purchase #4 $175.59   8.546%   $190.5959   $190.60   $190.60   $190.60  
  Purchase #5 $204.78   11.315%   $227.9509   $227.95   $227.95   $228.00  
  Purchase #6 $9.85   8.571%   $10.6942   $10.69   $10.70   $10.70  
  Purchase #7 $60.96   8.266%   $65.999   $66.00   $66.00   $66.00  
  7 purchase totals = $985.22       $1,055.0769   $1,055.08   $1,055.10   $1,055.10