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 $94.95   3.396%   $98.1745   $98.17   $98.15   $98.20  
  Purchase #2 $98.27   5.453%   $103.6287   $103.63   $103.65   $103.60  
  Purchase #3 $99.43   7.226%   $106.6148   $106.61   $106.60   $106.60  
  Purchase #4 $58.68   8.392%   $63.6044   $63.60   $63.60   $63.60  
  Purchase #5 $221.77   4.691%   $232.1732   $232.17   $232.15   $232.20  
  Purchase #6 $89.75   3.713%   $93.0824   $93.08   $93.10   $93.10  
  Purchase #7 $183.98   6.475%   $195.8927   $195.89   $195.90   $195.90  
  7 purchase totals = $846.83       $893.1707   $893.15   $893.15   $893.20