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	$148.67	6.386%	$158.1641	$158.16	$158.15	$158.20
Purchase #2	$189.83	3.808%	$197.0587	$197.06	$197.05	$197.10
Purchase #3	$30.91	9.314%	$33.789	$33.79	$33.80	$33.80
Purchase #4	$120.28	9.322%	$131.4925	$131.49	$131.50	$131.50
Purchase #5	$131.73	12.220%	$147.8274	$147.83	$147.85	$147.80
Purchase #6	$33.75	11.411%	$37.6012	$37.60	$37.60	$37.60
Purchase #7	$112.81	3.476%	$116.7313	$116.73	$116.75	$116.70
7 purchase totals =	$767.98		$822.6642	$822.66	$822.70	$822.70