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 $232.85   13.770%   $264.9134   $264.91   $264.90   $264.90  
  Purchase #2 $179.57   6.750%   $191.691   $191.69   $191.70   $191.70  
  Purchase #3 $49.75   3.251%   $51.3674   $51.37   $51.35   $51.40  
  Purchase #4 $130.42   5.457%   $137.537   $137.54   $137.55   $137.50  
  Purchase #5 $123.29   10.541%   $136.286   $136.29   $136.30   $136.30  
  Purchase #6 $14.41   8.678%   $15.6605   $15.66   $15.65   $15.70  
  Purchase #7 $95.87   10.303%   $105.7475   $105.75   $105.75   $105.70  
  7 purchase totals = $826.16       $903.2028   $903.21   $903.20   $903.20