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 $76.27   8.282%   $82.5867   $82.59   $82.60   $82.60  
  Purchase #2 $171.97   5.327%   $181.1308   $181.13   $181.15   $181.10  
  Purchase #3 $218.63   12.201%   $245.305   $245.31   $245.30   $245.30  
  Purchase #4 $69.54   7.539%   $74.7826   $74.78   $74.80   $74.80  
  Purchase #5 $9.64   3.868%   $10.0129   $10.01   $10.00   $10.00  
  Purchase #6 $21.99   13.857%   $25.0372   $25.04   $25.05   $25.00  
  Purchase #7 $140.47   4.145%   $146.2925   $146.29   $146.30   $146.30  
  7 purchase totals = $708.51       $765.1477   $765.15   $765.20   $765.10