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	$184.35	4.762%	$193.1287	$193.13	$193.15	$193.10
Purchase #2	$45.68	10.480%	$50.4673	$50.47	$50.45	$50.50
Purchase #3	$149.82	10.453%	$165.4807	$165.48	$165.50	$165.50
Purchase #4	$170.76	13.300%	$193.4711	$193.47	$193.45	$193.50
Purchase #5	$145.49	8.241%	$157.4798	$157.48	$157.50	$157.50
Purchase #6	$42.42	12.867%	$47.8782	$47.88	$47.90	$47.90
Purchase #7	$46.30	13.510%	$52.5551	$52.56	$52.55	$52.60
7 purchase totals =	$784.82		$860.4609	$860.47	$860.50	$860.60