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 $22.95   11.826%   $25.6641   $25.66   $25.65   $25.70  
  Purchase #2 $87.40   7.151%   $93.65   $93.65   $93.65   $93.70  
  Purchase #3 $187.67   9.865%   $206.1836   $206.18   $206.20   $206.20  
  Purchase #4 $206.28   9.250%   $225.3609   $225.36   $225.35   $225.40  
  Purchase #5 $125.95   12.178%   $141.2882   $141.29   $141.30   $141.30  
  Purchase #6 $205.41   9.465%   $224.8521   $224.85   $224.85   $224.90  
  Purchase #7 $49.31   13.311%   $55.8737   $55.87   $55.85   $55.90  
  7 purchase totals = $884.97       $972.8726   $972.86   $972.85   $973.10