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	$100.83	12.388%	$113.3208	$113.32	$113.30	$113.30
Purchase #2	$162.81	4.447%	$170.0502	$170.05	$170.05	$170.10
Purchase #3	$84.65	6.144%	$89.8509	$89.85	$89.85	$89.90
Purchase #4	$52.45	13.476%	$59.5182	$59.52	$59.50	$59.50
Purchase #5	$163.74	12.378%	$184.0077	$184.01	$184.00	$184.00
Purchase #6	$99.28	13.251%	$112.4356	$112.44	$112.45	$112.40
Purchase #7	$216.84	11.741%	$242.2992	$242.30	$242.30	$242.30
7 purchase totals =	$880.60		$971.4826	$971.49	$971.45	$971.50