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 $250.67   5.227%   $263.7725   $263.77   $263.75   $263.80  
  Purchase #2 $199.94   9.311%   $218.5564   $218.56   $218.55   $218.60  
  Purchase #3 $124.79   6.144%   $132.4571   $132.46   $132.45   $132.50  
  Purchase #4 $177.70   10.249%   $195.9125   $195.91   $195.90   $195.90  
  Purchase #5 $225.64   4.303%   $235.3493   $235.35   $235.35   $235.30  
  Purchase #6 $157.61   4.536%   $164.7592   $164.76   $164.75   $164.80  
  Purchase #7 $223.26   13.128%   $252.5696   $252.57   $252.55   $252.60  
  7 purchase totals = $1,359.61       $1,463.3766   $1,463.38   $1,463.30   $1,463.50