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 $41.44   5.153%   $43.5754   $43.58   $43.60   $43.60  
  Purchase #2 $114.57   12.815%   $129.2521   $129.25   $129.25   $129.30  
  Purchase #3 $11.33   6.396%   $12.0547   $12.05   $12.05   $12.10  
  Purchase #4 $159.44   11.806%   $178.2635   $178.26   $178.25   $178.30  
  Purchase #5 $130.71   11.200%   $145.3495   $145.35   $145.35   $145.30  
  Purchase #6 $153.49   12.176%   $172.1789   $172.18   $172.20   $172.20  
  Purchase #7 $220.78   13.768%   $251.177   $251.18   $251.20   $251.20  
  7 purchase totals = $831.76       $931.8511   $931.85   $931.90   $932.00