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 $164.39   7.643%   $176.9543   $176.95   $176.95   $177.00  
  Purchase #2 $228.47   12.837%   $257.7987   $257.80   $257.80   $257.80  
  Purchase #3 $136.30   13.117%   $154.1785   $154.18   $154.20   $154.20  
  Purchase #4 $238.98   6.211%   $253.823   $253.82   $253.80   $253.80  
  Purchase #5 $216.93   10.255%   $239.1762   $239.18   $239.20   $239.20  
  Purchase #6 $61.89   11.256%   $68.8563   $68.86   $68.85   $68.90  
  Purchase #7 $181.75   12.197%   $203.918   $203.92   $203.90   $203.90  
  7 purchase totals = $1,228.71       $1,354.7050   $1,354.71   $1,354.70   $1,354.80