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	$68.72	12.792%	$77.5107	$77.51	$77.50	$77.50
Purchase #2	$248.79	10.765%	$275.5722	$275.57	$275.55	$275.60
Purchase #3	$59.60	8.374%	$64.5909	$64.59	$64.60	$64.60
Purchase #4	$133.80	9.764%	$146.8642	$146.86	$146.85	$146.90
Purchase #5	$99.52	4.118%	$103.6182	$103.62	$103.60	$103.60
Purchase #6	$35.26	11.131%	$39.1848	$39.18	$39.20	$39.20
Purchase #7	$154.71	3.436%	$160.0258	$160.03	$160.05	$160.00
7 purchase totals =	$800.40		$867.3668	$867.36	$867.35	$867.40