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 $246.98   6.712%   $263.5573   $263.56   $263.55   $263.60  
  Purchase #2 $34.25   4.575%   $35.8169   $35.82   $35.80   $35.80  
  Purchase #3 $133.45   4.513%   $139.4726   $139.47   $139.45   $139.50  
  Purchase #4 $72.29   7.723%   $77.873   $77.87   $77.85   $77.90  
  Purchase #5 $98.86   3.102%   $101.9266   $101.93   $101.95   $101.90  
  Purchase #6 $244.44   8.401%   $264.9754   $264.98   $265.00   $265.00  
  Purchase #7 $230.75   8.214%   $249.7038   $249.70   $249.70   $249.70  
  7 purchase totals = $1,061.02       $1,133.3256   $1,133.33   $1,133.30   $1,133.40