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 $243.49   13.338%   $275.9667   $275.97   $275.95   $276.00  
  Purchase #2 $182.69   5.429%   $192.6082   $192.61   $192.60   $192.60  
  Purchase #3 $90.26   7.691%   $97.2019   $97.20   $97.20   $97.20  
  Purchase #4 $209.77   10.819%   $232.465   $232.47   $232.45   $232.50  
  Purchase #5 $148.59   10.130%   $163.6422   $163.64   $163.65   $163.60  
  Purchase #6 $201.40   7.213%   $215.927   $215.93   $215.95   $215.90  
  Purchase #7 $155.34   6.657%   $165.681   $165.68   $165.70   $165.70  
  7 purchase totals = $1,231.54       $1,343.4920   $1,343.50   $1,343.50   $1,343.50