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	$191.96	4.483%	$200.5656	$200.57	$200.55	$200.60
Purchase #2	$110.30	12.413%	$123.9915	$123.99	$124.00	$124.00
Purchase #3	$242.54	13.656%	$275.6613	$275.66	$275.65	$275.70
Purchase #4	$110.74	5.571%	$116.9093	$116.91	$116.90	$116.90
Purchase #5	$37.35	8.762%	$40.6226	$40.62	$40.60	$40.60
Purchase #6	$90.91	9.723%	$99.7492	$99.75	$99.75	$99.70
Purchase #7	$146.36	9.621%	$160.4413	$160.44	$160.45	$160.40
7 purchase totals =	$930.16		$1,017.9408	$1,017.94	$1,017.90	$1,017.90