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 $67.26   9.194%   $73.4439   $73.44   $73.45   $73.40  
  Purchase #2 $242.37   8.360%   $262.6321   $262.63   $262.65   $262.60  
  Purchase #3 $49.68   4.512%   $51.9216   $51.92   $51.90   $51.90  
  Purchase #4 $31.89   8.757%   $34.6826   $34.68   $34.70   $34.70  
  Purchase #5 $18.87   3.458%   $19.5225   $19.52   $19.50   $19.50  
  Purchase #6 $119.54   12.349%   $134.302   $134.30   $134.30   $134.30  
  Purchase #7 $150.49   5.683%   $159.0423   $159.04   $159.05   $159.00  
  7 purchase totals = $680.10       $735.5470   $735.53   $735.55   $735.40