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 $127.29   5.346%   $134.0949   $134.09   $134.10   $134.10  
  Purchase #2 $236.64   4.455%   $247.1823   $247.18   $247.20   $247.20  
  Purchase #3 $55.84   9.588%   $61.1939   $61.19   $61.20   $61.20  
  Purchase #4 $77.69   5.838%   $82.2255   $82.23   $82.25   $82.20  
  Purchase #5 $192.65   11.346%   $214.5081   $214.51   $214.50   $214.50  
  Purchase #6 $24.54   9.142%   $26.7834   $26.78   $26.80   $26.80  
  Purchase #7 $236.38   10.407%   $260.9801   $260.98   $261.00   $261.00  
  7 purchase totals = $951.03       $1,026.9682   $1,026.96   $1,027.05   $1,027.00