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 $59.37   7.817%   $64.011   $64.01   $64.00   $64.00  
  Purchase #2 $238.27   4.753%   $249.595   $249.60   $249.60   $249.60  
  Purchase #3 $93.99   6.669%   $100.2582   $100.26   $100.25   $100.30  
  Purchase #4 $157.57   8.382%   $170.7775   $170.78   $170.80   $170.80  
  Purchase #5 $86.54   3.261%   $89.3621   $89.36   $89.35   $89.40  
  Purchase #6 $218.63   3.472%   $226.2208   $226.22   $226.20   $226.20  
  Purchase #7 $67.64   3.527%   $70.0257   $70.03   $70.05   $70.00  
  7 purchase totals = $922.01       $970.2503   $970.26   $970.25   $970.30