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	$93.66	6.657%	$99.8949	$99.89	$99.90	$99.90
Purchase #2	$16.92	13.587%	$19.2189	$19.22	$19.20	$19.20
Purchase #3	$81.54	9.669%	$89.4241	$89.42	$89.40	$89.40
Purchase #4	$118.85	7.355%	$127.5914	$127.59	$127.60	$127.60
Purchase #5	$221.46	9.374%	$242.2197	$242.22	$242.20	$242.20
Purchase #6	$129.62	5.475%	$136.7167	$136.72	$136.70	$136.70
Purchase #7	$202.58	8.210%	$219.2118	$219.21	$219.20	$219.20
7 purchase totals =	$864.63		$934.2775	$934.27	$934.20	$934.20