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 $32.68   6.796%   $34.9009   $34.90   $34.90   $34.90  
  Purchase #2 $149.96   11.295%   $166.898   $166.90   $166.90   $166.90  
  Purchase #3 $107.94   12.805%   $121.7617   $121.76   $121.75   $121.80  
  Purchase #4 $155.85   13.788%   $177.3386   $177.34   $177.35   $177.30  
  Purchase #5 $65.96   11.266%   $73.3911   $73.39   $73.40   $73.40  
  Purchase #6 $119.55   9.342%   $130.7184   $130.72   $130.70   $130.70  
  Purchase #7 $114.99   3.496%   $119.0101   $119.01   $119.00   $119.00  
  7 purchase totals = $746.93       $824.0188   $824.02   $824.00   $824.00