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 $131.67   12.202%   $147.7364   $147.74   $147.75   $147.70  
  Purchase #2 $110.36   13.314%   $125.0533   $125.05   $125.05   $125.10  
  Purchase #3 $21.46   12.537%   $24.1504   $24.15   $24.15   $24.20  
  Purchase #4 $179.47   7.389%   $192.731   $192.73   $192.75   $192.70  
  Purchase #5 $232.99   6.800%   $248.8333   $248.83   $248.85   $248.80  
  Purchase #6 $52.93   5.721%   $55.9581   $55.96   $55.95   $56.00  
  Purchase #7 $241.49   6.515%   $257.2231   $257.22   $257.20   $257.20  
  7 purchase totals = $970.37       $1,051.6856   $1,051.68   $1,051.70   $1,051.70