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 $17.88   6.617%   $19.0631   $19.06   $19.05   $19.10  
  Purchase #2 $242.26   12.544%   $272.6491   $272.65   $272.65   $272.60  
  Purchase #3 $215.76   4.325%   $225.0916   $225.09   $225.10   $225.10  
  Purchase #4 $159.71   6.353%   $169.8564   $169.86   $169.85   $169.90  
  Purchase #5 $61.65   5.357%   $64.9526   $64.95   $64.95   $65.00  
  Purchase #6 $177.41   8.754%   $192.9405   $192.94   $192.95   $192.90  
  Purchase #7 $142.30   13.871%   $162.0384   $162.04   $162.05   $162.00  
  7 purchase totals = $1,016.97       $1,106.5917   $1,106.59   $1,106.60   $1,106.60