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 $201.37   12.372%   $226.2835   $226.28   $226.30   $226.30  
  Purchase #2 $31.90   3.305%   $32.9543   $32.95   $32.95   $33.00  
  Purchase #3 $104.96   10.171%   $115.6355   $115.64   $115.65   $115.60  
  Purchase #4 $42.80   10.377%   $47.2414   $47.24   $47.25   $47.20  
  Purchase #5 $162.57   3.548%   $168.338   $168.34   $168.35   $168.30  
  Purchase #6 $244.61   12.409%   $274.9637   $274.96   $274.95   $275.00  
  Purchase #7 $174.69   13.654%   $198.5422   $198.54   $198.55   $198.50  
  7 purchase totals = $962.90       $1,063.9586   $1,063.95   $1,064.00   $1,063.90