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 $246.65   5.418%   $260.0135   $260.01   $260.00   $260.00  
  Purchase #2 $70.31   11.113%   $78.1236   $78.12   $78.10   $78.10  
  Purchase #3 $65.76   11.321%   $73.2047   $73.20   $73.20   $73.20  
  Purchase #4 $18.41   8.113%   $19.9036   $19.90   $19.90   $19.90  
  Purchase #5 $53.55   13.841%   $60.9619   $60.96   $60.95   $61.00  
  Purchase #6 $131.27   3.691%   $136.1152   $136.12   $136.10   $136.10  
  Purchase #7 $161.27   4.808%   $169.0239   $169.02   $169.00   $169.00  
  7 purchase totals = $747.22       $797.3464   $797.33   $797.25   $797.30