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	$227.44	4.775%	$238.3003	$238.30	$238.30	$238.30
Purchase #2	$34.66	8.487%	$37.6016	$37.60	$37.60	$37.60
Purchase #3	$134.41	11.503%	$149.8712	$149.87	$149.85	$149.90
Purchase #4	$169.37	4.455%	$176.9154	$176.92	$176.90	$176.90
Purchase #5	$83.77	3.694%	$86.8645	$86.86	$86.85	$86.90
Purchase #6	$172.72	13.732%	$196.4379	$196.44	$196.45	$196.40
Purchase #7	$242.75	10.860%	$269.1127	$269.11	$269.10	$269.10
7 purchase totals =	$1,065.12		$1,155.1036	$1,155.10	$1,155.05	$1,155.10