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	$244.70	12.713%	$275.8087	$275.81	$275.80	$275.80
Purchase #2	$57.94	13.777%	$65.9224	$65.92	$65.90	$65.90
Purchase #3	$250.44	5.530%	$264.2893	$264.29	$264.30	$264.30
Purchase #4	$100.37	12.649%	$113.0658	$113.07	$113.05	$113.10
Purchase #5	$84.94	6.235%	$90.236	$90.24	$90.25	$90.20
Purchase #6	$76.85	4.783%	$80.5257	$80.53	$80.55	$80.50
Purchase #7	$98.94	12.455%	$111.263	$111.26	$111.25	$111.30
7 purchase totals =	$914.18		$1,001.1109	$1,001.12	$1,001.10	$1,001.10