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	$79.79	12.247%	$89.5619	$89.56	$89.55	$89.60
Purchase #2	$10.54	12.300%	$11.8364	$11.84	$11.85	$11.80
Purchase #3	$91.79	8.674%	$99.7519	$99.75	$99.75	$99.80
Purchase #4	$184.86	5.667%	$195.336	$195.34	$195.35	$195.30
Purchase #5	$113.97	8.340%	$123.4751	$123.48	$123.50	$123.50
Purchase #6	$149.52	6.427%	$159.1297	$159.13	$159.15	$159.10
Purchase #7	$97.32	9.859%	$106.9148	$106.91	$106.90	$106.90
7 purchase totals =	$727.79		$786.0058	$786.01	$786.05	$786.00