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 $58.77   11.213%   $65.3599   $65.36   $65.35   $65.40  
  Purchase #2 $187.51   6.357%   $199.43   $199.43   $199.45   $199.40  
  Purchase #3 $41.29   9.862%   $45.362   $45.36   $45.35   $45.40  
  Purchase #4 $105.95   10.768%   $117.3587   $117.36   $117.35   $117.40  
  Purchase #5 $199.67   6.277%   $212.2033   $212.20   $212.20   $212.20  
  Purchase #6 $105.62   9.167%   $115.3022   $115.30   $115.30   $115.30  
  Purchase #7 $9.97   10.455%   $11.0124   $11.01   $11.00   $11.00  
  7 purchase totals = $708.78       $766.0285   $766.02   $766.00   $766.10