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	$79.77	10.261%	$87.9552	$87.96	$87.95	$88.00
Purchase #2	$40.54	3.834%	$42.0943	$42.09	$42.10	$42.10
Purchase #3	$219.76	8.608%	$238.6769	$238.68	$238.70	$238.70
Purchase #4	$148.84	13.267%	$168.5866	$168.59	$168.60	$168.60
Purchase #5	$59.53	13.461%	$67.5433	$67.54	$67.55	$67.50
Purchase #6	$98.50	6.222%	$104.6287	$104.63	$104.65	$104.60
Purchase #7	$18.84	4.220%	$19.635	$19.64	$19.65	$19.60
7 purchase totals =	$665.78		$729.1200	$729.13	$729.20	$729.10