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 $224.35   11.368%   $249.8541   $249.85   $249.85   $249.90  
  Purchase #2 $190.76   6.346%   $202.8656   $202.87   $202.85   $202.90  
  Purchase #3 $92.53   5.551%   $97.6663   $97.67   $97.65   $97.70  
  Purchase #4 $13.42   9.763%   $14.7302   $14.73   $14.75   $14.70  
  Purchase #5 $237.91   11.494%   $265.2554   $265.26   $265.25   $265.30  
  Purchase #6 $101.68   4.228%   $105.979   $105.98   $106.00   $106.00  
  Purchase #7 $114.99   5.573%   $121.3984   $121.40   $121.40   $121.40  
  7 purchase totals = $975.64       $1,057.7490   $1,057.76   $1,057.75   $1,057.90