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 $185.49   8.862%   $201.9281   $201.93   $201.95   $201.90  
  Purchase #2 $124.91   6.185%   $132.6357   $132.64   $132.65   $132.60  
  Purchase #3 $104.74   13.353%   $118.7259   $118.73   $118.75   $118.70  
  Purchase #4 $155.88   13.233%   $176.5076   $176.51   $176.50   $176.50  
  Purchase #5 $238.40   13.404%   $270.3551   $270.36   $270.35   $270.40  
  Purchase #6 $228.66   7.208%   $245.1418   $245.14   $245.15   $245.10  
  Purchase #7 $204.63   4.160%   $213.1426   $213.14   $213.15   $213.10  
  7 purchase totals = $1,242.71       $1,358.4368   $1,358.45   $1,358.50   $1,358.30