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 $56.25   8.749%   $61.1713   $61.17   $61.15   $61.20  
  Purchase #2 $231.81   12.204%   $260.1001   $260.10   $260.10   $260.10  
  Purchase #3 $111.35   5.343%   $117.2994   $117.30   $117.30   $117.30  
  Purchase #4 $163.64   13.223%   $185.2781   $185.28   $185.30   $185.30  
  Purchase #5 $16.94   12.617%   $19.0773   $19.08   $19.10   $19.10  
  Purchase #6 $218.33   7.177%   $233.9995   $234.00   $234.00   $234.00  
  Purchase #7 $110.69   6.250%   $117.6081   $117.61   $117.60   $117.60  
  7 purchase totals = $909.01       $994.5338   $994.54   $994.55   $994.60