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 $200.26   5.626%   $211.5266   $211.53   $211.55   $211.50  
  Purchase #2 $154.29   8.801%   $167.8691   $167.87   $167.85   $167.90  
  Purchase #3 $121.81   4.507%   $127.3   $127.30   $127.30   $127.30  
  Purchase #4 $32.63   6.341%   $34.6991   $34.70   $34.70   $34.70  
  Purchase #5 $160.95   4.233%   $167.763   $167.76   $167.75   $167.80  
  Purchase #6 $32.25   3.842%   $33.489   $33.49   $33.50   $33.50  
  Purchase #7 $6.47   4.285%   $6.7472   $6.75   $6.75   $6.70  
  7 purchase totals = $708.66       $749.3940   $749.40   $749.40   $749.40