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 $216.54   9.426%   $236.9511   $236.95   $236.95   $237.00  
  Purchase #2 $140.25   12.461%   $157.7266   $157.73   $157.75   $157.70  
  Purchase #3 $227.27   12.156%   $254.8969   $254.90   $254.90   $254.90  
  Purchase #4 $122.30   4.311%   $127.5724   $127.57   $127.55   $127.60  
  Purchase #5 $111.94   11.610%   $124.9362   $124.94   $124.95   $124.90  
  Purchase #6 $192.45   3.700%   $199.5707   $199.57   $199.55   $199.60  
  Purchase #7 $58.72   6.466%   $62.5168   $62.52   $62.50   $62.50  
  7 purchase totals = $1,069.47       $1,164.1707   $1,164.18   $1,164.15   $1,164.20