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	$248.77	8.440%	$269.7662	$269.77	$269.75	$269.80
Purchase #2	$131.37	11.290%	$146.2017	$146.20	$146.20	$146.20
Purchase #3	$104.42	5.574%	$110.2404	$110.24	$110.25	$110.20
Purchase #4	$96.27	9.479%	$105.3954	$105.40	$105.40	$105.40
Purchase #5	$79.88	13.516%	$90.6766	$90.68	$90.70	$90.70
Purchase #6	$240.78	13.535%	$273.3696	$273.37	$273.35	$273.40
Purchase #7	$21.48	4.678%	$22.4848	$22.48	$22.50	$22.50
7 purchase totals =	$922.97		$1,018.1347	$1,018.14	$1,018.15	$1,018.20