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 $24.76   7.831%   $26.699   $26.70   $26.70   $26.70  
  Purchase #2 $194.76   7.259%   $208.8976   $208.90   $208.90   $208.90  
  Purchase #3 $79.56   11.151%   $88.4317   $88.43   $88.45   $88.40  
  Purchase #4 $41.48   12.785%   $46.7832   $46.78   $46.80   $46.80  
  Purchase #5 $246.93   8.790%   $268.6351   $268.64   $268.65   $268.60  
  Purchase #6 $151.83   9.465%   $166.2007   $166.20   $166.20   $166.20  
  Purchase #7 $47.45   9.362%   $51.8923   $51.89   $51.90   $51.90  
  7 purchase totals = $786.77       $857.5396   $857.54   $857.60   $857.50