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 $227.67   9.648%   $249.6356   $249.64   $249.65   $249.60  
  Purchase #2 $72.59   4.200%   $75.6388   $75.64   $75.65   $75.60  
  Purchase #3 $112.65   12.362%   $126.5758   $126.58   $126.60   $126.60  
  Purchase #4 $232.29   11.230%   $258.3762   $258.38   $258.40   $258.40  
  Purchase #5 $67.41   13.692%   $76.6398   $76.64   $76.65   $76.60  
  Purchase #6 $27.40   7.610%   $29.4851   $29.49   $29.50   $29.50  
  Purchase #7 $187.84   10.706%   $207.9502   $207.95   $207.95   $208.00  
  7 purchase totals = $927.85       $1,024.3015   $1,024.32   $1,024.40   $1,024.30