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	$137.52	5.696%	$145.3531	$145.35	$145.35	$145.40
Purchase #2	$212.66	5.717%	$224.8178	$224.82	$224.80	$224.80
Purchase #3	$106.86	5.536%	$112.7758	$112.78	$112.80	$112.80
Purchase #4	$209.28	9.167%	$228.4647	$228.46	$228.45	$228.50
Purchase #5	$99.86	13.440%	$113.2812	$113.28	$113.30	$113.30
Purchase #6	$75.82	8.793%	$82.4869	$82.49	$82.50	$82.50
Purchase #7	$29.71	8.656%	$32.2817	$32.28	$32.30	$32.30
7 purchase totals =	$871.71		$939.4612	$939.46	$939.50	$939.60