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 $234.78   11.671%   $262.1812   $262.18   $262.20   $262.20  
  Purchase #2 $210.79   9.845%   $231.5423   $231.54   $231.55   $231.50  
  Purchase #3 $111.66   3.221%   $115.2566   $115.26   $115.25   $115.30  
  Purchase #4 $173.99   8.788%   $189.2802   $189.28   $189.30   $189.30  
  Purchase #5 $125.92   12.657%   $141.8577   $141.86   $141.85   $141.90  
  Purchase #6 $9.49   5.717%   $10.0325   $10.03   $10.05   $10.00  
  Purchase #7 $16.80   13.341%   $19.0413   $19.04   $19.05   $19.00  
  7 purchase totals = $883.43       $969.1918   $969.19   $969.25   $969.20