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 $58.47   5.309%   $61.5742   $61.57   $61.55   $61.60  
  Purchase #2 $229.54   7.480%   $246.7096   $246.71   $246.70   $246.70  
  Purchase #3 $11.64   9.212%   $12.7123   $12.71   $12.70   $12.70  
  Purchase #4 $26.55   8.689%   $28.8569   $28.86   $28.85   $28.90  
  Purchase #5 $158.99   4.795%   $166.6136   $166.61   $166.60   $166.60  
  Purchase #6 $129.90   10.873%   $144.024   $144.02   $144.00   $144.00  
  Purchase #7 $212.63   5.509%   $224.3438   $224.34   $224.35   $224.30  
  7 purchase totals = $827.72       $884.8344   $884.82   $884.75   $884.80