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 $29.35   5.192%   $30.8739   $30.87   $30.85   $30.90  
  Purchase #2 $58.61   9.430%   $64.1369   $64.14   $64.15   $64.10  
  Purchase #3 $89.56   12.305%   $100.5804   $100.58   $100.60   $100.60  
  Purchase #4 $12.66   4.749%   $13.2612   $13.26   $13.25   $13.30  
  Purchase #5 $165.47   10.696%   $183.1687   $183.17   $183.15   $183.20  
  Purchase #6 $110.65   7.311%   $118.7396   $118.74   $118.75   $118.70  
  Purchase #7 $176.44   13.103%   $199.5589   $199.56   $199.55   $199.60  
  7 purchase totals = $642.74       $710.3196   $710.32   $710.30   $710.40