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	$187.67	13.735%	$213.4465	$213.45	$213.45	$213.40
Purchase #2	$247.94	12.318%	$278.4812	$278.48	$278.50	$278.50
Purchase #3	$196.73	9.543%	$215.5039	$215.50	$215.50	$215.50
Purchase #4	$112.56	10.420%	$124.2888	$124.29	$124.30	$124.30
Purchase #5	$82.34	10.252%	$90.7815	$90.78	$90.80	$90.80
Purchase #6	$217.42	9.524%	$238.1271	$238.13	$238.15	$238.10
Purchase #7	$229.72	3.766%	$238.3713	$238.37	$238.35	$238.40
7 purchase totals =	$1,274.38		$1,399.0003	$1,399.00	$1,399.05	$1,399.00