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 $115.94   13.832%   $131.9768   $131.98   $132.00   $132.00  
  Purchase #2 $20.47   7.203%   $21.9445   $21.94   $21.95   $21.90  
  Purchase #3 $86.81   10.156%   $95.6264   $95.63   $95.65   $95.60  
  Purchase #4 $107.59   4.673%   $112.6177   $112.62   $112.60   $112.60  
  Purchase #5 $75.85   5.365%   $79.9194   $79.92   $79.90   $79.90  
  Purchase #6 $85.40   13.364%   $96.8129   $96.81   $96.80   $96.80  
  Purchase #7 $214.43   4.671%   $224.446   $224.45   $224.45   $224.40  
  7 purchase totals = $706.49       $763.3437   $763.35   $763.35   $763.20