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	$91.44	13.779%	$104.0395	$104.04	$104.05	$104.00
Purchase #2	$210.65	11.350%	$234.5588	$234.56	$234.55	$234.60
Purchase #3	$173.55	3.579%	$179.7614	$179.76	$179.75	$179.80
Purchase #4	$62.58	4.323%	$65.2853	$65.29	$65.30	$65.30
Purchase #5	$47.82	12.458%	$53.7774	$53.78	$53.80	$53.80
Purchase #6	$198.51	11.126%	$220.5962	$220.60	$220.60	$220.60
Purchase #7	$59.63	13.705%	$67.8023	$67.80	$67.80	$67.80
7 purchase totals =	$844.18		$925.8209	$925.83	$925.85	$925.90