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 $154.97   5.716%   $163.8281   $163.83   $163.85   $163.80  
  Purchase #2 $108.83   10.868%   $120.6576   $120.66   $120.65   $120.70  
  Purchase #3 $181.26   8.445%   $196.5674   $196.57   $196.55   $196.60  
  Purchase #4 $163.26   8.283%   $176.7828   $176.78   $176.80   $176.80  
  Purchase #5 $244.62   10.726%   $270.8579   $270.86   $270.85   $270.90  
  Purchase #6 $198.73   5.535%   $209.7297   $209.73   $209.75   $209.70  
  Purchase #7 $125.28   6.353%   $133.239   $133.24   $133.25   $133.20  
  7 purchase totals = $1,176.95       $1,271.6625   $1,271.67   $1,271.70   $1,271.70