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 $115.91   6.240%   $123.1428   $123.14   $123.15   $123.10  
  Purchase #2 $75.60   3.447%   $78.2059   $78.21   $78.20   $78.20  
  Purchase #3 $151.39   12.802%   $170.7709   $170.77   $170.75   $170.80  
  Purchase #4 $240.64   6.742%   $256.8639   $256.86   $256.85   $256.90  
  Purchase #5 $107.49   5.667%   $113.5815   $113.58   $113.60   $113.60  
  Purchase #6 $148.67   6.748%   $158.7023   $158.70   $158.70   $158.70  
  Purchase #7 $194.45   5.423%   $204.995   $205.00   $205.00   $205.00  
  7 purchase totals = $1,034.15       $1,106.2623   $1,106.26   $1,106.25   $1,106.30