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	$55.94	3.581%	$57.9432	$57.94	$57.95	$57.90
Purchase #2	$115.30	13.204%	$130.5242	$130.52	$130.50	$130.50
Purchase #3	$60.53	3.667%	$62.7496	$62.75	$62.75	$62.70
Purchase #4	$117.30	5.282%	$123.4958	$123.50	$123.50	$123.50
Purchase #5	$149.34	10.804%	$165.4747	$165.47	$165.45	$165.50
Purchase #6	$178.57	3.845%	$185.436	$185.44	$185.45	$185.40
Purchase #7	$244.28	6.252%	$259.5524	$259.55	$259.55	$259.60
7 purchase totals =	$921.26		$985.1759	$985.17	$985.15	$985.10