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 $67.57   12.609%   $76.0899   $76.09   $76.10   $76.10  
  Purchase #2 $245.25   12.657%   $276.2913   $276.29   $276.30   $276.30  
  Purchase #3 $194.41   6.363%   $206.7803   $206.78   $206.80   $206.80  
  Purchase #4 $149.51   9.741%   $164.0738   $164.07   $164.05   $164.10  
  Purchase #5 $204.63   13.253%   $231.7496   $231.75   $231.75   $231.70  
  Purchase #6 $217.68   9.752%   $238.9082   $238.91   $238.90   $238.90  
  Purchase #7 $53.48   7.316%   $57.3926   $57.39   $57.40   $57.40  
  7 purchase totals = $1,132.53       $1,251.2857   $1,251.28   $1,251.30   $1,251.30