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	$122.89	3.614%	$127.3312	$127.33	$127.35	$127.30
Purchase #2	$85.41	7.788%	$92.0617	$92.06	$92.05	$92.10
Purchase #3	$151.71	8.695%	$164.9012	$164.90	$164.90	$164.90
Purchase #4	$18.30	8.581%	$19.8703	$19.87	$19.85	$19.90
Purchase #5	$214.67	12.528%	$241.5639	$241.56	$241.55	$241.60
Purchase #6	$31.42	3.691%	$32.5797	$32.58	$32.60	$32.60
Purchase #7	$149.70	3.259%	$154.5787	$154.58	$154.60	$154.60
7 purchase totals =	$774.10		$832.8867	$832.88	$832.90	$833.00