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	$122.61	9.561%	$134.3327	$134.33	$134.35	$134.30
Purchase #2	$205.95	11.280%	$229.1812	$229.18	$229.20	$229.20
Purchase #3	$245.78	13.627%	$279.2724	$279.27	$279.25	$279.30
Purchase #4	$32.76	8.820%	$35.6494	$35.65	$35.65	$35.60
Purchase #5	$224.95	11.511%	$250.844	$250.84	$250.85	$250.80
Purchase #6	$132.95	3.341%	$137.3919	$137.39	$137.40	$137.40
Purchase #7	$213.84	9.240%	$233.5988	$233.60	$233.60	$233.60
7 purchase totals =	$1,178.84		$1,300.2704	$1,300.26	$1,300.30	$1,300.20