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	$6.86	3.200%	$7.0795	$7.08	$7.10	$7.10
Purchase #2	$155.29	3.279%	$160.382	$160.38	$160.40	$160.40
Purchase #3	$248.63	10.803%	$275.4895	$275.49	$275.50	$275.50
Purchase #4	$79.37	4.766%	$83.1528	$83.15	$83.15	$83.20
Purchase #5	$91.88	8.713%	$99.8855	$99.89	$99.90	$99.90
Purchase #6	$212.68	7.116%	$227.8143	$227.81	$227.80	$227.80
Purchase #7	$202.52	11.798%	$226.4133	$226.41	$226.40	$226.40
7 purchase totals =	$997.23		$1,080.2169	$1,080.21	$1,080.25	$1,080.30