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 $53.81   13.683%   $61.1728   $61.17   $61.15   $61.20  
  Purchase #2 $68.86   10.694%   $76.2239   $76.22   $76.20   $76.20  
  Purchase #3 $118.77   4.205%   $123.7643   $123.76   $123.75   $123.80  
  Purchase #4 $108.63   12.322%   $122.0154   $122.02   $122.00   $122.00  
  Purchase #5 $90.31   13.641%   $102.6292   $102.63   $102.65   $102.60  
  Purchase #6 $24.46   7.639%   $26.3285   $26.33   $26.35   $26.30  
  Purchase #7 $235.93   3.677%   $244.6051   $244.61   $244.60   $244.60  
  7 purchase totals = $700.77       $756.7392   $756.74   $756.70   $756.70