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 $32.41   11.244%   $36.0542   $36.05   $36.05   $36.10  
  Purchase #2 $65.71   5.570%   $69.37   $69.37   $69.35   $69.40  
  Purchase #3 $96.78   7.733%   $104.264   $104.26   $104.25   $104.30  
  Purchase #4 $83.96   10.706%   $92.9488   $92.95   $92.95   $92.90  
  Purchase #5 $56.55   3.685%   $58.6339   $58.63   $58.65   $58.60  
  Purchase #6 $230.54   4.516%   $240.9512   $240.95   $240.95   $241.00  
  Purchase #7 $44.99   5.769%   $47.5855   $47.59   $47.60   $47.60  
  7 purchase totals = $610.94       $649.8076   $649.80   $649.80   $649.90