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	$63.83	8.851%	$69.4796	$69.48	$69.50	$69.50
Purchase #2	$214.63	12.164%	$240.7376	$240.74	$240.75	$240.70
Purchase #3	$55.66	7.483%	$59.825	$59.83	$59.85	$59.80
Purchase #4	$101.84	13.218%	$115.3012	$115.30	$115.30	$115.30
Purchase #5	$111.48	11.502%	$124.3024	$124.30	$124.30	$124.30
Purchase #6	$158.41	13.384%	$179.6116	$179.61	$179.60	$179.60
Purchase #7	$118.91	10.234%	$131.0792	$131.08	$131.10	$131.10
7 purchase totals =	$824.76		$920.3366	$920.34	$920.40	$920.30