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 $68.82   10.813%   $76.2615   $76.26   $76.25   $76.30  
  Purchase #2 $34.29   10.325%   $37.8304   $37.83   $37.85   $37.80  
  Purchase #3 $10.43   3.662%   $10.8119   $10.81   $10.80   $10.80  
  Purchase #4 $234.79   11.419%   $261.6007   $261.60   $261.60   $261.60  
  Purchase #5 $79.67   12.409%   $89.5563   $89.56   $89.55   $89.60  
  Purchase #6 $122.92   8.102%   $132.879   $132.88   $132.90   $132.90  
  Purchase #7 $183.97   5.432%   $193.9633   $193.96   $193.95   $194.00  
  7 purchase totals = $734.89       $802.9031   $802.90   $802.90   $803.00