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	$18.50	7.636%	$19.9127	$19.91	$19.90	$19.90
Purchase #2	$227.39	11.514%	$253.5717	$253.57	$253.55	$253.60
Purchase #3	$100.92	12.318%	$113.3513	$113.35	$113.35	$113.40
Purchase #4	$101.27	9.723%	$111.1165	$111.12	$111.10	$111.10
Purchase #5	$209.85	4.873%	$220.076	$220.08	$220.10	$220.10
Purchase #6	$96.38	13.412%	$109.3065	$109.31	$109.30	$109.30
Purchase #7	$49.53	12.797%	$55.8684	$55.87	$55.85	$55.90
7 purchase totals =	$803.84		$883.2031	$883.21	$883.15	$883.30