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 $112.69   4.728%   $118.018   $118.02   $118.00   $118.00  
  Purchase #2 $249.62   6.490%   $265.8203   $265.82   $265.80   $265.80  
  Purchase #3 $164.90   5.113%   $173.3313   $173.33   $173.35   $173.30  
  Purchase #4 $13.55   11.434%   $15.0993   $15.10   $15.10   $15.10  
  Purchase #5 $83.75   10.127%   $92.2314   $92.23   $92.25   $92.20  
  Purchase #6 $216.97   10.335%   $239.3938   $239.39   $239.40   $239.40  
  Purchase #7 $84.65   11.412%   $94.3103   $94.31   $94.30   $94.30  
  7 purchase totals = $926.13       $998.2044   $998.20   $998.20   $998.10