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	$112.27	7.293%	$120.4579	$120.46	$120.45	$120.50
Purchase #2	$25.82	11.213%	$28.7152	$28.72	$28.70	$28.70
Purchase #3	$248.77	8.473%	$269.8483	$269.85	$269.85	$269.80
Purchase #4	$139.39	10.326%	$153.7834	$153.78	$153.80	$153.80
Purchase #5	$238.71	10.793%	$264.474	$264.47	$264.45	$264.50
Purchase #6	$64.41	11.137%	$71.5833	$71.58	$71.60	$71.60
Purchase #7	$79.39	4.774%	$83.1801	$83.18	$83.20	$83.20
7 purchase totals =	$908.76		$992.0422	$992.04	$992.05	$992.10