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	$11.80	7.722%	$12.7112	$12.71	$12.70	$12.70
Purchase #2	$67.39	4.266%	$70.2649	$70.26	$70.25	$70.30
Purchase #3	$139.61	4.692%	$146.1605	$146.16	$146.15	$146.20
Purchase #4	$151.67	4.356%	$158.2767	$158.28	$158.30	$158.30
Purchase #5	$99.30	10.420%	$109.6471	$109.65	$109.65	$109.60
Purchase #6	$133.41	12.510%	$150.0996	$150.10	$150.10	$150.10
Purchase #7	$70.28	12.780%	$79.2618	$79.26	$79.25	$79.30
7 purchase totals =	$673.46		$726.4218	$726.42	$726.40	$726.50