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 $65.54   10.341%   $72.3175   $72.32   $72.30   $72.30  
  Purchase #2 $98.31   13.582%   $111.6625   $111.66   $111.65   $111.70  
  Purchase #3 $27.97   10.267%   $30.8417   $30.84   $30.85   $30.80  
  Purchase #4 $94.63   13.747%   $107.6388   $107.64   $107.65   $107.60  
  Purchase #5 $88.83   5.831%   $94.0097   $94.01   $94.00   $94.00  
  Purchase #6 $178.43   12.225%   $200.2431   $200.24   $200.25   $200.20  
  Purchase #7 $96.93   11.417%   $107.9965   $108.00   $108.00   $108.00  
  7 purchase totals = $650.64       $724.7098   $724.71   $724.70   $724.60