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	$194.34	13.280%	$220.1484	$220.15	$220.15	$220.10
Purchase #2	$146.33	7.801%	$157.7452	$157.75	$157.75	$157.70
Purchase #3	$36.66	9.707%	$40.2186	$40.22	$40.20	$40.20
Purchase #4	$31.62	12.647%	$35.619	$35.62	$35.60	$35.60
Purchase #5	$225.52	10.362%	$248.8884	$248.89	$248.90	$248.90
Purchase #6	$117.37	5.494%	$123.8183	$123.82	$123.80	$123.80
Purchase #7	$89.94	7.257%	$96.4669	$96.47	$96.45	$96.50
7 purchase totals =	$841.78		$922.9048	$922.92	$922.85	$922.80