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 $82.80   11.754%   $92.5323   $92.53   $92.55   $92.50  
  Purchase #2 $67.57   11.195%   $75.1345   $75.13   $75.15   $75.10  
  Purchase #3 $126.44   6.397%   $134.5284   $134.53   $134.55   $134.50  
  Purchase #4 $18.64   8.607%   $20.2443   $20.24   $20.25   $20.20  
  Purchase #5 $232.27   6.554%   $247.493   $247.49   $247.50   $247.50  
  Purchase #6 $156.94   7.669%   $168.9757   $168.98   $169.00   $169.00  
  Purchase #7 $241.38   13.635%   $274.2922   $274.29   $274.30   $274.30  
  7 purchase totals = $926.04       $1,013.2004   $1,013.19   $1,013.30   $1,013.10