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	$188.29	11.274%	$209.5178	$209.52	$209.50	$209.50
Purchase #2	$234.81	3.103%	$242.0962	$242.10	$242.10	$242.10
Purchase #3	$17.34	12.695%	$19.5413	$19.54	$19.55	$19.50
Purchase #4	$30.36	7.690%	$32.6947	$32.69	$32.70	$32.70
Purchase #5	$100.61	11.166%	$111.8441	$111.84	$111.85	$111.80
Purchase #6	$111.51	10.763%	$123.5118	$123.51	$123.50	$123.50
Purchase #7	$110.58	10.348%	$122.0228	$122.02	$122.00	$122.00
7 purchase totals =	$793.50		$861.2287	$861.22	$861.20	$861.10