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 $86.66   13.218%   $98.1147   $98.11   $98.10   $98.10  
  Purchase #2 $8.85   4.650%   $9.2615   $9.26   $9.25   $9.30  
  Purchase #3 $64.53   8.462%   $69.9905   $69.99   $70.00   $70.00  
  Purchase #4 $234.47   7.329%   $251.6543   $251.65   $251.65   $251.70  
  Purchase #5 $134.76   7.681%   $145.1109   $145.11   $145.10   $145.10  
  Purchase #6 $131.53   13.159%   $148.838   $148.84   $148.85   $148.80  
  Purchase #7 $240.95   8.182%   $260.6645   $260.66   $260.65   $260.70  
  7 purchase totals = $901.75       $983.6344   $983.62   $983.60   $983.70