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	$178.98	4.863%	$187.6838	$187.68	$187.70	$187.70
Purchase #2	$50.85	11.404%	$56.6489	$56.65	$56.65	$56.60
Purchase #3	$91.49	9.639%	$100.3087	$100.31	$100.30	$100.30
Purchase #4	$24.95	12.788%	$28.1406	$28.14	$28.15	$28.10
Purchase #5	$52.48	8.746%	$57.0699	$57.07	$57.05	$57.10
Purchase #6	$79.56	13.764%	$90.5106	$90.51	$90.50	$90.50
Purchase #7	$221.90	11.659%	$247.7713	$247.77	$247.75	$247.80
7 purchase totals =	$700.21		$768.1338	$768.13	$768.10	$768.10