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	$146.48	13.817%	$166.7191	$166.72	$166.70	$166.70
Purchase #2	$149.28	8.832%	$162.4644	$162.46	$162.45	$162.50
Purchase #3	$216.80	11.815%	$242.4149	$242.41	$242.40	$242.40
Purchase #4	$151.83	3.313%	$156.8601	$156.86	$156.85	$156.90
Purchase #5	$39.38	11.246%	$43.8087	$43.81	$43.80	$43.80
Purchase #6	$79.31	12.488%	$89.2142	$89.21	$89.20	$89.20
Purchase #7	$20.42	11.424%	$22.7528	$22.75	$22.75	$22.80
7 purchase totals =	$803.50		$884.2342	$884.22	$884.15	$884.30