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 $86.49   8.278%   $93.6496   $93.65   $93.65   $93.60  
  Purchase #2 $75.72   6.426%   $80.5858   $80.59   $80.60   $80.60  
  Purchase #3 $61.72   13.845%   $70.2651   $70.27   $70.25   $70.30  
  Purchase #4 $159.41   10.642%   $176.3744   $176.37   $176.35   $176.40  
  Purchase #5 $110.71   7.706%   $119.2413   $119.24   $119.25   $119.20  
  Purchase #6 $237.87   4.828%   $249.3544   $249.35   $249.35   $249.40  
  Purchase #7 $108.96   6.308%   $115.8332   $115.83   $115.85   $115.80  
  7 purchase totals = $840.88       $905.3038   $905.30   $905.30   $905.30