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 $198.78   3.193%   $205.127   $205.13   $205.15   $205.10  
  Purchase #2 $151.91   3.266%   $156.8714   $156.87   $156.85   $156.90  
  Purchase #3 $244.38   11.136%   $271.5942   $271.59   $271.60   $271.60  
  Purchase #4 $213.28   13.796%   $242.7041   $242.70   $242.70   $242.70  
  Purchase #5 $207.57   11.161%   $230.7369   $230.74   $230.75   $230.70  
  Purchase #6 $201.40   12.829%   $227.2376   $227.24   $227.25   $227.20  
  Purchase #7 $135.49   13.136%   $153.288   $153.29   $153.30   $153.30  
  7 purchase totals = $1,352.81       $1,487.5592   $1,487.56   $1,487.60   $1,487.50