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 $217.84   8.156%   $235.607   $235.61   $235.60   $235.60  
  Purchase #2 $68.36   3.462%   $70.7266   $70.73   $70.75   $70.70  
  Purchase #3 $48.31   9.417%   $52.8594   $52.86   $52.85   $52.90  
  Purchase #4 $7.83   4.479%   $8.1807   $8.18   $8.20   $8.20  
  Purchase #5 $215.32   5.311%   $226.7556   $226.76   $226.75   $226.80  
  Purchase #6 $12.77   8.772%   $13.8902   $13.89   $13.90   $13.90  
  Purchase #7 $78.86   10.222%   $86.9211   $86.92   $86.90   $86.90  
  7 purchase totals = $649.29       $694.9406   $694.95   $694.95   $695.00