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	$28.73	10.550%	$31.761	$31.76	$31.75	$31.80
Purchase #2	$127.64	11.384%	$142.1705	$142.17	$142.15	$142.20
Purchase #3	$64.39	4.754%	$67.4511	$67.45	$67.45	$67.50
Purchase #4	$152.85	13.163%	$172.9696	$172.97	$172.95	$173.00
Purchase #5	$83.89	5.329%	$88.3605	$88.36	$88.35	$88.40
Purchase #6	$76.34	12.132%	$85.6016	$85.60	$85.60	$85.60
Purchase #7	$195.61	7.203%	$209.6998	$209.70	$209.70	$209.70
7 purchase totals =	$729.45		$798.0141	$798.01	$797.95	$798.20