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 $118.37   13.261%   $134.067   $134.07   $134.05   $134.10  
  Purchase #2 $79.67   8.302%   $86.2842   $86.28   $86.30   $86.30  
  Purchase #3 $119.95   7.787%   $129.2905   $129.29   $129.30   $129.30  
  Purchase #4 $237.61   6.698%   $253.5251   $253.53   $253.55   $253.50  
  Purchase #5 $53.39   4.835%   $55.9714   $55.97   $55.95   $56.00  
  Purchase #6 $68.89   7.548%   $74.0898   $74.09   $74.10   $74.10  
  Purchase #7 $11.92   9.119%   $13.007   $13.01   $13.00   $13.00  
  7 purchase totals = $689.80       $746.2350   $746.24   $746.25   $746.30