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 $53.69   9.780%   $58.9409   $58.94   $58.95   $58.90  
  Purchase #2 $210.96   10.620%   $233.364   $233.36   $233.35   $233.40  
  Purchase #3 $67.28   4.454%   $70.2767   $70.28   $70.30   $70.30  
  Purchase #4 $195.38   10.244%   $215.3947   $215.39   $215.40   $215.40  
  Purchase #5 $118.87   13.303%   $134.6833   $134.68   $134.70   $134.70  
  Purchase #6 $172.56   10.460%   $190.6098   $190.61   $190.60   $190.60  
  Purchase #7 $105.73   11.685%   $118.0846   $118.08   $118.10   $118.10  
  7 purchase totals = $924.47       $1,021.3540   $1,021.34   $1,021.40   $1,021.40