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 $131.95   10.761%   $146.1491   $146.15   $146.15   $146.10  
  Purchase #2 $203.88   7.108%   $218.3718   $218.37   $218.35   $218.40  
  Purchase #3 $42.58   12.617%   $47.9523   $47.95   $47.95   $48.00  
  Purchase #4 $164.32   10.728%   $181.9482   $181.95   $181.95   $181.90  
  Purchase #5 $66.32   4.148%   $69.071   $69.07   $69.05   $69.10  
  Purchase #6 $77.66   8.550%   $84.2999   $84.30   $84.30   $84.30  
  Purchase #7 $20.80   4.137%   $21.6605   $21.66   $21.65   $21.70  
  7 purchase totals = $707.51       $769.4528   $769.45   $769.40   $769.50