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 $151.86   8.303%   $164.4689   $164.47   $164.45   $164.50  
  Purchase #2 $151.82   3.763%   $157.533   $157.53   $157.55   $157.50  
  Purchase #3 $235.29   5.193%   $247.5086   $247.51   $247.50   $247.50  
  Purchase #4 $71.35   6.783%   $76.1897   $76.19   $76.20   $76.20  
  Purchase #5 $223.33   9.733%   $245.0667   $245.07   $245.05   $245.10  
  Purchase #6 $243.78   9.862%   $267.8216   $267.82   $267.80   $267.80  
  Purchase #7 $176.65   13.649%   $200.761   $200.76   $200.75   $200.80  
  7 purchase totals = $1,254.08       $1,359.3495   $1,359.35   $1,359.30   $1,359.40