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 $194.62   6.104%   $206.4996   $206.50   $206.50   $206.50  
  Purchase #2 $81.48   10.223%   $89.8097   $89.81   $89.80   $89.80  
  Purchase #3 $238.81   6.660%   $254.7147   $254.71   $254.70   $254.70  
  Purchase #4 $222.53   4.221%   $231.923   $231.92   $231.90   $231.90  
  Purchase #5 $113.75   5.374%   $119.8629   $119.86   $119.85   $119.90  
  Purchase #6 $222.63   3.671%   $230.8027   $230.80   $230.80   $230.80  
  Purchase #7 $228.35   6.565%   $243.3412   $243.34   $243.35   $243.30  
  7 purchase totals = $1,302.17       $1,376.9538   $1,376.94   $1,376.90   $1,376.90