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	$85.29	6.535%	$90.8637	$90.86	$90.85	$90.90
Purchase #2	$90.56	3.698%	$93.9089	$93.91	$93.90	$93.90
Purchase #3	$15.68	13.283%	$17.7628	$17.76	$17.75	$17.80
Purchase #4	$113.70	11.589%	$126.8767	$126.88	$126.90	$126.90
Purchase #5	$89.44	8.147%	$96.7267	$96.73	$96.75	$96.70
Purchase #6	$140.90	10.748%	$156.0439	$156.04	$156.05	$156.00
Purchase #7	$112.29	3.661%	$116.4009	$116.40	$116.40	$116.40
7 purchase totals =	$647.86		$698.5836	$698.58	$698.60	$698.60