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 $53.46   13.524%   $60.6899   $60.69   $60.70   $60.70  
  Purchase #2 $185.27   11.216%   $206.0499   $206.05   $206.05   $206.00  
  Purchase #3 $94.92   4.123%   $98.8336   $98.83   $98.85   $98.80  
  Purchase #4 $70.55   4.617%   $73.8073   $73.81   $73.80   $73.80  
  Purchase #5 $95.86   7.361%   $102.9163   $102.92   $102.90   $102.90  
  Purchase #6 $142.87   4.514%   $149.3192   $149.32   $149.30   $149.30  
  Purchase #7 $137.31   3.521%   $142.1447   $142.14   $142.15   $142.10  
  7 purchase totals = $780.24       $833.7609   $833.76   $833.75   $833.60