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 $204.97   13.746%   $233.1452   $233.15   $233.15   $233.10  
  Purchase #2 $242.73   3.518%   $251.2692   $251.27   $251.25   $251.30  
  Purchase #3 $76.76   6.246%   $81.5544   $81.55   $81.55   $81.60  
  Purchase #4 $211.68   6.610%   $225.672   $225.67   $225.65   $225.70  
  Purchase #5 $229.61   10.482%   $253.6777   $253.68   $253.70   $253.70  
  Purchase #6 $44.66   5.142%   $46.9564   $46.96   $46.95   $47.00  
  Purchase #7 $159.77   10.613%   $176.7264   $176.73   $176.75   $176.70  
  7 purchase totals = $1,170.18       $1,269.0013   $1,269.01   $1,269.00   $1,269.10