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	$173.34	13.264%	$196.3318	$196.33	$196.35	$196.30
Purchase #2	$108.25	6.113%	$114.8673	$114.87	$114.85	$114.90
Purchase #3	$83.40	5.841%	$88.2714	$88.27	$88.25	$88.30
Purchase #4	$11.46	3.335%	$11.8422	$11.84	$11.85	$11.80
Purchase #5	$141.73	5.437%	$149.4359	$149.44	$149.45	$149.40
Purchase #6	$24.36	10.497%	$26.9171	$26.92	$26.90	$26.90
Purchase #7	$196.80	13.431%	$223.2322	$223.23	$223.25	$223.20
7 purchase totals =	$739.34		$810.8979	$810.90	$810.90	$810.80