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	$227.91	13.760%	$259.2704	$259.27	$259.25	$259.30
Purchase #2	$145.81	4.666%	$152.6135	$152.61	$152.60	$152.60
Purchase #3	$210.56	12.280%	$236.4168	$236.42	$236.40	$236.40
Purchase #4	$192.34	8.559%	$208.8024	$208.80	$208.80	$208.80
Purchase #5	$171.60	11.806%	$191.8591	$191.86	$191.85	$191.90
Purchase #6	$183.39	6.422%	$195.1673	$195.17	$195.15	$195.20
Purchase #7	$86.57	3.725%	$89.7947	$89.79	$89.80	$89.80
7 purchase totals =	$1,218.18		$1,333.9242	$1,333.92	$1,333.85	$1,334.00