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 $12.61   11.774%   $14.0947   $14.09   $14.10   $14.10  
  Purchase #2 $233.25   13.580%   $264.9254   $264.93   $264.95   $264.90  
  Purchase #3 $58.97   8.795%   $64.1564   $64.16   $64.15   $64.20  
  Purchase #4 $153.30   5.549%   $161.8066   $161.81   $161.80   $161.80  
  Purchase #5 $172.95   12.222%   $194.0879   $194.09   $194.10   $194.10  
  Purchase #6 $230.54   11.286%   $256.5587   $256.56   $256.55   $256.60  
  Purchase #7 $205.98   10.315%   $227.2268   $227.23   $227.25   $227.20  
  7 purchase totals = $1,067.60       $1,182.8565   $1,182.87   $1,182.90   $1,182.90