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	$246.61	10.219%	$271.8111	$271.81	$271.80	$271.80
Purchase #2	$53.44	5.739%	$56.5069	$56.51	$56.50	$56.50
Purchase #3	$46.69	6.540%	$49.7435	$49.74	$49.75	$49.70
Purchase #4	$55.41	12.426%	$62.2952	$62.30	$62.30	$62.30
Purchase #5	$211.60	10.781%	$234.4126	$234.41	$234.40	$234.40
Purchase #6	$165.47	12.344%	$185.8956	$185.90	$185.90	$185.90
Purchase #7	$9.78	7.185%	$10.4827	$10.48	$10.50	$10.50
7 purchase totals =	$789.00		$871.1476	$871.15	$871.15	$871.10