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 $202.65   10.346%   $223.6162   $223.62   $223.60   $223.60  
  Purchase #2 $215.89   3.387%   $223.2022   $223.20   $223.20   $223.20  
  Purchase #3 $103.83   10.555%   $114.7893   $114.79   $114.80   $114.80  
  Purchase #4 $15.92   8.445%   $17.2644   $17.26   $17.25   $17.30  
  Purchase #5 $50.94   8.487%   $55.2633   $55.26   $55.25   $55.30  
  Purchase #6 $181.32   3.851%   $188.3026   $188.30   $188.30   $188.30  
  Purchase #7 $116.45   6.742%   $124.3011   $124.30   $124.30   $124.30  
  7 purchase totals = $887.00       $946.7391   $946.73   $946.70   $946.80