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 $225.80   6.171%   $239.7341   $239.73   $239.75   $239.70  
  Purchase #2 $173.45   12.638%   $195.3706   $195.37   $195.35   $195.40  
  Purchase #3 $68.33   6.837%   $73.0017   $73.00   $73.00   $73.00  
  Purchase #4 $52.61   3.532%   $54.4682   $54.47   $54.45   $54.50  
  Purchase #5 $71.64   3.175%   $73.9146   $73.91   $73.90   $73.90  
  Purchase #6 $248.55   9.795%   $272.8955   $272.90   $272.90   $272.90  
  Purchase #7 $53.75   5.748%   $56.8396   $56.84   $56.85   $56.80  
  7 purchase totals = $894.13       $966.2243   $966.22   $966.20   $966.20