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	$240.43	12.148%	$269.6374	$269.64	$269.65	$269.60
Purchase #2	$177.74	4.451%	$185.6512	$185.65	$185.65	$185.70
Purchase #3	$230.65	3.397%	$238.4852	$238.49	$238.50	$238.50
Purchase #4	$44.32	12.620%	$49.9132	$49.91	$49.90	$49.90
Purchase #5	$113.82	13.400%	$129.0719	$129.07	$129.05	$129.10
Purchase #6	$6.32	4.556%	$6.6079	$6.61	$6.60	$6.60
Purchase #7	$128.76	6.223%	$136.7727	$136.77	$136.75	$136.80
7 purchase totals =	$942.04		$1,016.1395	$1,016.14	$1,016.10	$1,016.20