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 $64.45   11.342%   $71.7599   $71.76   $71.75   $71.80  
  Purchase #2 $151.72   13.860%   $172.7484   $172.75   $172.75   $172.70  
  Purchase #3 $52.27   11.205%   $58.1269   $58.13   $58.15   $58.10  
  Purchase #4 $184.94   5.815%   $195.6943   $195.69   $195.70   $195.70  
  Purchase #5 $75.76   9.554%   $82.9981   $83.00   $83.00   $83.00  
  Purchase #6 $125.34   8.124%   $135.5226   $135.52   $135.50   $135.50  
  Purchase #7 $246.92   6.177%   $262.1722   $262.17   $262.15   $262.20  
  7 purchase totals = $901.40       $979.0224   $979.02   $979.00   $979.00