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 $107.26   11.152%   $119.2216   $119.22   $119.20   $119.20  
  Purchase #2 $50.92   11.133%   $56.5889   $56.59   $56.60   $56.60  
  Purchase #3 $31.97   11.227%   $35.5593   $35.56   $35.55   $35.60  
  Purchase #4 $67.36   6.452%   $71.7061   $71.71   $71.70   $71.70  
  Purchase #5 $233.62   4.377%   $243.8455   $243.85   $243.85   $243.80  
  Purchase #6 $68.89   8.335%   $74.632   $74.63   $74.65   $74.60  
  Purchase #7 $81.67   4.871%   $85.6481   $85.65   $85.65   $85.60  
  7 purchase totals = $641.69       $687.2015   $687.21   $687.20   $687.10