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	$76.63	7.178%	$82.1305	$82.13	$82.15	$82.10
Purchase #2	$100.35	6.582%	$106.955	$106.96	$106.95	$107.00
Purchase #3	$176.56	6.709%	$188.4054	$188.41	$188.40	$188.40
Purchase #4	$148.28	3.597%	$153.6136	$153.61	$153.60	$153.60
Purchase #5	$112.31	3.503%	$116.2442	$116.24	$116.25	$116.20
Purchase #6	$146.71	13.223%	$166.1095	$166.11	$166.10	$166.10
Purchase #7	$19.61	8.709%	$21.3178	$21.32	$21.30	$21.30
7 purchase totals =	$780.45		$834.7760	$834.78	$834.75	$834.70