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	$18.26	10.758%	$20.2244	$20.22	$20.20	$20.20
Purchase #2	$136.27	4.402%	$142.2686	$142.27	$142.25	$142.30
Purchase #3	$77.71	3.673%	$80.5643	$80.56	$80.55	$80.60
Purchase #4	$200.63	11.613%	$223.9292	$223.93	$223.95	$223.90
Purchase #5	$215.69	10.377%	$238.0722	$238.07	$238.05	$238.10
Purchase #6	$213.62	10.346%	$235.7211	$235.72	$235.70	$235.70
Purchase #7	$38.40	6.211%	$40.785	$40.79	$40.80	$40.80
7 purchase totals =	$900.58		$981.5648	$981.56	$981.50	$981.60