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	$6.81	10.856%	$7.5493	$7.55	$7.55	$7.50
Purchase #2	$235.82	13.782%	$268.3207	$268.32	$268.30	$268.30
Purchase #3	$221.69	11.825%	$247.9048	$247.90	$247.90	$247.90
Purchase #4	$227.80	4.687%	$238.477	$238.48	$238.50	$238.50
Purchase #5	$173.57	10.388%	$191.6005	$191.60	$191.60	$191.60
Purchase #6	$176.58	11.735%	$197.3017	$197.30	$197.30	$197.30
Purchase #7	$142.88	4.598%	$149.4496	$149.45	$149.45	$149.40
7 purchase totals =	$1,185.15		$1,300.6036	$1,300.60	$1,300.60	$1,300.50