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 $82.66   4.228%   $86.1549   $86.15   $86.15   $86.20  
  Purchase #2 $59.54   4.213%   $62.0484   $62.05   $62.05   $62.00  
  Purchase #3 $154.48   11.639%   $172.4599   $172.46   $172.45   $172.50  
  Purchase #4 $85.34   10.322%   $94.1488   $94.15   $94.15   $94.10  
  Purchase #5 $72.45   4.437%   $75.6646   $75.66   $75.65   $75.70  
  Purchase #6 $208.92   6.573%   $222.6523   $222.65   $222.65   $222.70  
  Purchase #7 $222.97   8.370%   $241.6326   $241.63   $241.65   $241.60  
  7 purchase totals = $886.36       $954.7615   $954.75   $954.75   $954.80