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 $118.58   6.719%   $126.5474   $126.55   $126.55   $126.50  
  Purchase #2 $65.47   12.299%   $73.5222   $73.52   $73.50   $73.50  
  Purchase #3 $42.40   13.309%   $48.043   $48.04   $48.05   $48.00  
  Purchase #4 $55.87   10.188%   $61.562   $61.56   $61.55   $61.60  
  Purchase #5 $166.33   7.318%   $178.502   $178.50   $178.50   $178.50  
  Purchase #6 $221.86   3.852%   $230.406   $230.41   $230.40   $230.40  
  Purchase #7 $205.30   11.832%   $229.5911   $229.59   $229.60   $229.60  
  7 purchase totals = $875.81       $948.1737   $948.17   $948.15   $948.10