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	$57.67	3.644%	$59.7715	$59.77	$59.75	$59.80
Purchase #2	$242.26	12.142%	$271.6752	$271.68	$271.70	$271.70
Purchase #3	$54.28	13.417%	$61.5627	$61.56	$61.55	$61.60
Purchase #4	$168.91	9.784%	$185.4362	$185.44	$185.45	$185.40
Purchase #5	$186.65	3.674%	$193.5075	$193.51	$193.50	$193.50
Purchase #6	$111.25	11.462%	$124.0015	$124.00	$124.00	$124.00
Purchase #7	$112.42	7.460%	$120.8065	$120.81	$120.80	$120.80
7 purchase totals =	$933.44		$1,016.7611	$1,016.77	$1,016.75	$1,016.80