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	$90.72	12.738%	$102.2759	$102.28	$102.30	$102.30
Purchase #2	$228.84	9.589%	$250.7835	$250.78	$250.80	$250.80
Purchase #3	$11.61	12.758%	$13.0912	$13.09	$13.10	$13.10
Purchase #4	$234.93	6.679%	$250.621	$250.62	$250.60	$250.60
Purchase #5	$94.84	4.741%	$99.3364	$99.34	$99.35	$99.30
Purchase #6	$125.49	5.119%	$131.9138	$131.91	$131.90	$131.90
Purchase #7	$129.82	7.607%	$139.6954	$139.70	$139.70	$139.70
7 purchase totals =	$916.25		$987.7172	$987.72	$987.75	$987.70