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 $201.39   10.554%   $222.6447   $222.64   $222.65   $222.60  
  Purchase #2 $64.87   3.201%   $66.9465   $66.95   $66.95   $66.90  
  Purchase #3 $58.98   6.704%   $62.934   $62.93   $62.95   $62.90  
  Purchase #4 $139.81   6.104%   $148.344   $148.34   $148.35   $148.30  
  Purchase #5 $250.63   7.595%   $269.6653   $269.67   $269.65   $269.70  
  Purchase #6 $171.29   8.485%   $185.824   $185.82   $185.80   $185.80  
  Purchase #7 $8.79   8.506%   $9.5377   $9.54   $9.55   $9.50  
  7 purchase totals = $895.76       $965.8962   $965.89   $965.90   $965.70