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 $113.81   11.751%   $127.1838   $127.18   $127.20   $127.20  
  Purchase #2 $117.59   7.420%   $126.3152   $126.32   $126.30   $126.30  
  Purchase #3 $242.32   12.578%   $272.799   $272.80   $272.80   $272.80  
  Purchase #4 $129.86   3.756%   $134.7375   $134.74   $134.75   $134.70  
  Purchase #5 $238.40   6.211%   $253.207   $253.21   $253.20   $253.20  
  Purchase #6 $179.44   11.860%   $200.7216   $200.72   $200.70   $200.70  
  Purchase #7 $154.71   4.369%   $161.4693   $161.47   $161.45   $161.50  
  7 purchase totals = $1,176.13       $1,276.4334   $1,276.44   $1,276.40   $1,276.40