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 $232.48   12.105%   $260.6217   $260.62   $260.60   $260.60  
  Purchase #2 $69.50   12.167%   $77.9561   $77.96   $77.95   $78.00  
  Purchase #3 $60.40   9.803%   $66.321   $66.32   $66.30   $66.30  
  Purchase #4 $81.54   11.591%   $90.9913   $90.99   $91.00   $91.00  
  Purchase #5 $133.65   7.291%   $143.3944   $143.39   $143.40   $143.40  
  Purchase #6 $65.32   8.365%   $70.784   $70.78   $70.80   $70.80  
  Purchase #7 $232.78   3.214%   $240.2615   $240.26   $240.25   $240.30  
  7 purchase totals = $875.67       $950.3300   $950.32   $950.30   $950.40