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 $56.81   7.760%   $61.2185   $61.22   $61.20   $61.20  
  Purchase #2 $142.73   6.212%   $151.5964   $151.60   $151.60   $151.60  
  Purchase #3 $16.94   5.289%   $17.836   $17.84   $17.85   $17.80  
  Purchase #4 $223.35   7.192%   $239.4133   $239.41   $239.40   $239.40  
  Purchase #5 $51.27   8.465%   $55.61   $55.61   $55.60   $55.60  
  Purchase #6 $212.96   13.595%   $241.9119   $241.91   $241.90   $241.90  
  Purchase #7 $128.28   4.481%   $134.0282   $134.03   $134.05   $134.00  
  7 purchase totals = $832.34       $901.6143   $901.62   $901.60   $901.50