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	$209.52	10.316%	$231.1341	$231.13	$231.15	$231.10
Purchase #2	$80.87	10.866%	$89.6573	$89.66	$89.65	$89.70
Purchase #3	$250.59	10.608%	$277.1726	$277.17	$277.15	$277.20
Purchase #4	$6.41	11.279%	$7.133	$7.13	$7.15	$7.10
Purchase #5	$92.66	4.404%	$96.7407	$96.74	$96.75	$96.70
Purchase #6	$14.67	3.143%	$15.1311	$15.13	$15.15	$15.10
Purchase #7	$112.63	4.390%	$117.5745	$117.57	$117.55	$117.60
7 purchase totals =	$767.35		$834.5433	$834.53	$834.55	$834.50