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 $20.63   11.515%   $23.0055   $23.01   $23.00   $23.00  
  Purchase #2 $86.74   6.585%   $92.4518   $92.45   $92.45   $92.50  
  Purchase #3 $181.77   3.808%   $188.6918   $188.69   $188.70   $188.70  
  Purchase #4 $92.66   3.767%   $96.1505   $96.15   $96.15   $96.20  
  Purchase #5 $227.32   7.457%   $244.2713   $244.27   $244.25   $244.30  
  Purchase #6 $44.32   11.602%   $49.462   $49.46   $49.45   $49.50  
  Purchase #7 $54.65   9.645%   $59.921   $59.92   $59.90   $59.90  
  7 purchase totals = $708.09       $753.9539   $753.95   $753.90   $754.10