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 $68.30   7.160%   $73.1903   $73.19   $73.20   $73.20  
  Purchase #2 $110.85   13.463%   $125.7737   $125.77   $125.75   $125.80  
  Purchase #3 $243.29   3.141%   $250.9317   $250.93   $250.95   $250.90  
  Purchase #4 $80.43   13.397%   $91.2052   $91.21   $91.20   $91.20  
  Purchase #5 $101.25   7.227%   $108.5673   $108.57   $108.55   $108.60  
  Purchase #6 $88.29   9.200%   $96.4127   $96.41   $96.40   $96.40  
  Purchase #7 $112.29   7.873%   $121.1306   $121.13   $121.15   $121.10  
  7 purchase totals = $804.70       $867.2115   $867.21   $867.20   $867.20