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 $55.38   10.116%   $60.9822   $60.98   $61.00   $61.00  
  Purchase #2 $242.67   7.178%   $260.0889   $260.09   $260.10   $260.10  
  Purchase #3 $95.46   11.838%   $106.7606   $106.76   $106.75   $106.80  
  Purchase #4 $97.35   5.267%   $102.4774   $102.48   $102.50   $102.50  
  Purchase #5 $20.29   12.172%   $22.7597   $22.76   $22.75   $22.80  
  Purchase #6 $185.48   11.781%   $207.3314   $207.33   $207.35   $207.30  
  Purchase #7 $189.44   3.741%   $196.527   $196.53   $196.55   $196.50  
  7 purchase totals = $886.07       $956.9272   $956.93   $957.00   $957.00