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 $91.65   6.135%   $97.2727   $97.27   $97.25   $97.30  
  Purchase #2 $50.65   3.740%   $52.5443   $52.54   $52.55   $52.50  
  Purchase #3 $59.69   10.692%   $66.0721   $66.07   $66.05   $66.10  
  Purchase #4 $94.47   7.114%   $101.1906   $101.19   $101.20   $101.20  
  Purchase #5 $156.28   3.420%   $161.6248   $161.62   $161.60   $161.60  
  Purchase #6 $129.60   12.375%   $145.638   $145.64   $145.65   $145.60  
  Purchase #7 $165.92   5.596%   $175.2049   $175.20   $175.20   $175.20  
  7 purchase totals = $748.26       $799.5474   $799.53   $799.50   $799.50