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 $60.96   10.852%   $67.5754   $67.58   $67.60   $67.60  
  Purchase #2 $245.93   6.201%   $261.1801   $261.18   $261.20   $261.20  
  Purchase #3 $57.83   8.107%   $62.5183   $62.52   $62.50   $62.50  
  Purchase #4 $90.48   3.863%   $93.9752   $93.98   $94.00   $94.00  
  Purchase #5 $208.48   9.324%   $227.9187   $227.92   $227.90   $227.90  
  Purchase #6 $211.26   11.160%   $234.8366   $234.84   $234.85   $234.80  
  Purchase #7 $33.98   11.446%   $37.8694   $37.87   $37.85   $37.90  
  7 purchase totals = $908.92       $985.8737   $985.89   $985.90   $985.90