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 $227.66   8.207%   $246.3441   $246.34   $246.35   $246.30  
  Purchase #2 $233.83   12.423%   $262.8787   $262.88   $262.90   $262.90  
  Purchase #3 $140.87   10.797%   $156.0797   $156.08   $156.10   $156.10  
  Purchase #4 $116.46   7.328%   $124.9942   $124.99   $125.00   $125.00  
  Purchase #5 $134.33   9.858%   $147.5723   $147.57   $147.55   $147.60  
  Purchase #6 $65.63   4.814%   $68.7894   $68.79   $68.80   $68.80  
  Purchase #7 $199.41   9.744%   $218.8405   $218.84   $218.85   $218.80  
  7 purchase totals = $1,118.19       $1,225.4989   $1,225.49   $1,225.55   $1,225.50