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 $46.93   13.862%   $53.4354   $53.44   $53.45   $53.40  
  Purchase #2 $87.54   13.145%   $99.0471   $99.05   $99.05   $99.00  
  Purchase #3 $104.57   7.204%   $112.1032   $112.10   $112.10   $112.10  
  Purchase #4 $187.97   3.598%   $194.7332   $194.73   $194.75   $194.70  
  Purchase #5 $164.75   6.566%   $175.5675   $175.57   $175.55   $175.60  
  Purchase #6 $236.79   4.818%   $248.1985   $248.20   $248.20   $248.20  
  Purchase #7 $141.82   6.519%   $151.0652   $151.07   $151.05   $151.10  
  7 purchase totals = $970.37       $1,034.1501   $1,034.16   $1,034.15   $1,034.10