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 $119.93   11.713%   $133.9774   $133.98   $134.00   $134.00  
  Purchase #2 $46.69   4.277%   $48.6869   $48.69   $48.70   $48.70  
  Purchase #3 $22.83   9.684%   $25.0409   $25.04   $25.05   $25.00  
  Purchase #4 $231.79   7.196%   $248.4696   $248.47   $248.45   $248.50  
  Purchase #5 $206.66   11.204%   $229.8142   $229.81   $229.80   $229.80  
  Purchase #6 $106.83   5.747%   $112.9695   $112.97   $112.95   $113.00  
  Purchase #7 $96.72   7.262%   $103.7438   $103.74   $103.75   $103.70  
  7 purchase totals = $831.45       $902.7023   $902.70   $902.70   $902.70