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	$173.79	13.162%	$196.6642	$196.66	$196.65	$196.70
Purchase #2	$107.50	3.175%	$110.9131	$110.91	$110.90	$110.90
Purchase #3	$55.59	10.263%	$61.2952	$61.30	$61.30	$61.30
Purchase #4	$174.53	3.840%	$181.232	$181.23	$181.25	$181.20
Purchase #5	$185.61	4.147%	$193.3072	$193.31	$193.30	$193.30
Purchase #6	$37.35	9.156%	$40.7698	$40.77	$40.75	$40.80
Purchase #7	$90.47	7.147%	$96.9359	$96.94	$96.95	$96.90
7 purchase totals =	$824.84		$881.1174	$881.12	$881.10	$881.10