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 $156.92   3.398%   $162.2521   $162.25   $162.25   $162.30  
  Purchase #2 $244.99   8.766%   $266.4658   $266.47   $266.45   $266.50  
  Purchase #3 $184.57   11.578%   $205.9395   $205.94   $205.95   $205.90  
  Purchase #4 $53.71   5.275%   $56.5432   $56.54   $56.55   $56.50  
  Purchase #5 $246.44   12.191%   $276.4835   $276.48   $276.50   $276.50  
  Purchase #6 $108.57   3.185%   $112.028   $112.03   $112.05   $112.00  
  Purchase #7 $158.73   5.800%   $167.9363   $167.94   $167.95   $167.90  
  7 purchase totals = $1,153.93       $1,247.6484   $1,247.65   $1,247.70   $1,247.60