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 $72.42   13.294%   $82.0475   $82.05   $82.05   $82.00  
  Purchase #2 $110.61   13.869%   $125.9505   $125.95   $125.95   $126.00  
  Purchase #3 $197.57   13.618%   $224.4751   $224.48   $224.50   $224.50  
  Purchase #4 $128.61   8.465%   $139.4968   $139.50   $139.50   $139.50  
  Purchase #5 $25.86   13.502%   $29.3516   $29.35   $29.35   $29.40  
  Purchase #6 $86.62   10.378%   $95.6094   $95.61   $95.60   $95.60  
  Purchase #7 $212.90   9.492%   $233.1085   $233.11   $233.10   $233.10  
  7 purchase totals = $834.59       $930.0394   $930.05   $930.05   $930.10