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 $212.88   5.785%   $225.1951   $225.20   $225.20   $225.20  
  Purchase #2 $90.30   6.829%   $96.4666   $96.47   $96.45   $96.50  
  Purchase #3 $207.97   9.676%   $228.0932   $228.09   $228.10   $228.10  
  Purchase #4 $241.35   12.517%   $271.5598   $271.56   $271.55   $271.60  
  Purchase #5 $113.30   4.456%   $118.3486   $118.35   $118.35   $118.30  
  Purchase #6 $153.60   12.150%   $172.2624   $172.26   $172.25   $172.30  
  Purchase #7 $185.97   4.849%   $194.9877   $194.99   $195.00   $195.00  
  7 purchase totals = $1,205.37       $1,306.9134   $1,306.92   $1,306.90   $1,307.00