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	$143.67	13.305%	$162.7853	$162.79	$162.80	$162.80
Purchase #2	$56.35	3.512%	$58.329	$58.33	$58.35	$58.30
Purchase #3	$80.25	7.364%	$86.1596	$86.16	$86.15	$86.20
Purchase #4	$160.93	3.311%	$166.2584	$166.26	$166.25	$166.30
Purchase #5	$90.37	9.703%	$99.1386	$99.14	$99.15	$99.10
Purchase #6	$196.61	13.234%	$222.6294	$222.63	$222.65	$222.60
Purchase #7	$172.92	4.427%	$180.5752	$180.58	$180.60	$180.60
7 purchase totals =	$901.10		$975.8755	$975.89	$975.95	$975.90