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 $68.80   6.847%   $73.5107   $73.51   $73.50   $73.50  
  Purchase #2 $121.43   4.756%   $127.2052   $127.21   $127.20   $127.20  
  Purchase #3 $87.89   7.688%   $94.647   $94.65   $94.65   $94.60  
  Purchase #4 $233.82   9.557%   $256.1662   $256.17   $256.15   $256.20  
  Purchase #5 $242.50   11.842%   $271.2169   $271.22   $271.20   $271.20  
  Purchase #6 $148.44   6.140%   $157.5542   $157.55   $157.55   $157.60  
  Purchase #7 $82.50   11.537%   $92.018   $92.02   $92.00   $92.00  
  7 purchase totals = $985.38       $1,072.3182   $1,072.33   $1,072.25   $1,072.30