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 $93.54   3.762%   $97.059   $97.06   $97.05   $97.10  
  Purchase #2 $170.80   13.580%   $193.9946   $193.99   $194.00   $194.00  
  Purchase #3 $36.74   10.102%   $40.4515   $40.45   $40.45   $40.50  
  Purchase #4 $204.38   6.274%   $217.2028   $217.20   $217.20   $217.20  
  Purchase #5 $64.44   3.687%   $66.8159   $66.82   $66.80   $66.80  
  Purchase #6 $72.97   10.466%   $80.607   $80.61   $80.60   $80.60  
  Purchase #7 $124.60   9.532%   $136.4769   $136.48   $136.50   $136.50  
  7 purchase totals = $767.47       $832.6077   $832.61   $832.60   $832.70