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 $201.50   10.756%   $223.1733   $223.17   $223.15   $223.20  
  Purchase #2 $24.61   10.402%   $27.1699   $27.17   $27.15   $27.20  
  Purchase #3 $92.61   13.393%   $105.0133   $105.01   $105.00   $105.00  
  Purchase #4 $98.73   11.573%   $110.156   $110.16   $110.15   $110.20  
  Purchase #5 $70.74   7.645%   $76.1481   $76.15   $76.15   $76.10  
  Purchase #6 $49.64   11.236%   $55.2176   $55.22   $55.20   $55.20  
  Purchase #7 $70.64   11.795%   $78.972   $78.97   $78.95   $79.00  
  7 purchase totals = $608.47       $675.8502   $675.85   $675.75   $675.90