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 $42.26   4.662%   $44.2302   $44.23   $44.25   $44.20  
  Purchase #2 $94.84   3.262%   $97.9337   $97.93   $97.95   $97.90  
  Purchase #3 $153.38   11.137%   $170.4619   $170.46   $170.45   $170.50  
  Purchase #4 $232.43   9.513%   $254.5411   $254.54   $254.55   $254.50  
  Purchase #5 $118.93   13.351%   $134.8083   $134.81   $134.80   $134.80  
  Purchase #6 $105.42   11.311%   $117.3441   $117.34   $117.35   $117.30  
  Purchase #7 $138.51   13.720%   $157.5136   $157.51   $157.50   $157.50  
  7 purchase totals = $885.77       $976.8329   $976.82   $976.85   $976.70