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 $244.53   4.653%   $255.908   $255.91   $255.90   $255.90  
  Purchase #2 $44.97   12.675%   $50.6699   $50.67   $50.65   $50.70  
  Purchase #3 $212.82   9.488%   $233.0124   $233.01   $233.00   $233.00  
  Purchase #4 $163.30   4.182%   $170.1292   $170.13   $170.15   $170.10  
  Purchase #5 $121.95   12.794%   $137.5523   $137.55   $137.55   $137.60  
  Purchase #6 $160.55   13.161%   $181.68   $181.68   $181.70   $181.70  
  Purchase #7 $119.26   11.873%   $133.4197   $133.42   $133.40   $133.40  
  7 purchase totals = $1,067.38       $1,162.3715   $1,162.37   $1,162.35   $1,162.40