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 $240.49   5.713%   $254.2292   $254.23   $254.25   $254.20  
  Purchase #2 $86.96   10.245%   $95.8691   $95.87   $95.85   $95.90  
  Purchase #3 $10.82   4.241%   $11.2789   $11.28   $11.30   $11.30  
  Purchase #4 $222.69   6.362%   $236.8575   $236.86   $236.85   $236.90  
  Purchase #5 $151.88   11.185%   $168.8678   $168.87   $168.85   $168.90  
  Purchase #6 $56.59   7.703%   $60.9491   $60.95   $60.95   $60.90  
  Purchase #7 $194.41   9.358%   $212.6029   $212.60   $212.60   $212.60  
  7 purchase totals = $963.84       $1,040.6545   $1,040.66   $1,040.65   $1,040.70