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	$237.34	13.504%	$269.3904	$269.39	$269.40	$269.40
Purchase #2	$99.37	10.129%	$109.4352	$109.44	$109.45	$109.40
Purchase #3	$224.84	10.825%	$249.1789	$249.18	$249.20	$249.20
Purchase #4	$45.30	13.559%	$51.4422	$51.44	$51.45	$51.40
Purchase #5	$250.78	10.500%	$277.1119	$277.11	$277.10	$277.10
Purchase #6	$100.72	10.679%	$111.4759	$111.48	$111.50	$111.50
Purchase #7	$219.83	7.601%	$236.5393	$236.54	$236.55	$236.50
7 purchase totals =	$1,178.18		$1,304.5738	$1,304.58	$1,304.65	$1,304.50