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	$100.88	8.341%	$109.2944	$109.29	$109.30	$109.30
Purchase #2	$54.46	9.541%	$59.656	$59.66	$59.65	$59.70
Purchase #3	$84.89	13.243%	$96.132	$96.13	$96.15	$96.10
Purchase #4	$85.52	9.782%	$93.8856	$93.89	$93.90	$93.90
Purchase #5	$90.28	3.814%	$93.7233	$93.72	$93.70	$93.70
Purchase #6	$126.73	8.638%	$137.6769	$137.68	$137.70	$137.70
Purchase #7	$48.81	10.153%	$53.7657	$53.77	$53.75	$53.80
7 purchase totals =	$591.57		$644.1339	$644.14	$644.15	$644.20