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 $244.83   9.310%   $267.6237   $267.62   $267.60   $267.60  
  Purchase #2 $145.58   11.157%   $161.8224   $161.82   $161.80   $161.80  
  Purchase #3 $186.75   6.600%   $199.0755   $199.08   $199.10   $199.10  
  Purchase #4 $227.45   4.120%   $236.8209   $236.82   $236.80   $236.80  
  Purchase #5 $173.60   9.688%   $190.4184   $190.42   $190.40   $190.40  
  Purchase #6 $198.83   12.727%   $224.1351   $224.14   $224.15   $224.10  
  Purchase #7 $215.62   13.118%   $243.905   $243.91   $243.90   $243.90  
  7 purchase totals = $1,392.66       $1,523.8010   $1,523.81   $1,523.75   $1,523.70