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 $242.72   5.225%   $255.4021   $255.40   $255.40   $255.40  
  Purchase #2 $82.49   10.364%   $91.0393   $91.04   $91.05   $91.00  
  Purchase #3 $195.37   5.220%   $205.5683   $205.57   $205.55   $205.60  
  Purchase #4 $181.31   7.733%   $195.3307   $195.33   $195.35   $195.30  
  Purchase #5 $55.64   5.784%   $58.8582   $58.86   $58.85   $58.90  
  Purchase #6 $199.35   7.491%   $214.2833   $214.28   $214.30   $214.30  
  Purchase #7 $237.78   7.631%   $255.925   $255.93   $255.95   $255.90  
  7 purchase totals = $1,194.66       $1,276.4069   $1,276.41   $1,276.45   $1,276.40