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 $239.62   9.862%   $263.2513   $263.25   $263.25   $263.30  
  Purchase #2 $71.51   13.164%   $80.9236   $80.92   $80.90   $80.90  
  Purchase #3 $166.27   5.414%   $175.2719   $175.27   $175.25   $175.30  
  Purchase #4 $134.34   5.226%   $141.3606   $141.36   $141.35   $141.40  
  Purchase #5 $217.93   5.325%   $229.5348   $229.53   $229.55   $229.50  
  Purchase #6 $234.34   11.498%   $261.2844   $261.28   $261.30   $261.30  
  Purchase #7 $22.65   5.813%   $23.9666   $23.97   $23.95   $24.00  
  7 purchase totals = $1,086.66       $1,175.5932   $1,175.58   $1,175.55   $1,175.70