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	$247.31	6.580%	$263.583	$263.58	$263.60	$263.60
Purchase #2	$136.47	7.573%	$146.8049	$146.80	$146.80	$146.80
Purchase #3	$188.31	8.419%	$204.1638	$204.16	$204.15	$204.20
Purchase #4	$25.49	13.234%	$28.8633	$28.86	$28.85	$28.90
Purchase #5	$112.38	9.722%	$123.3056	$123.31	$123.30	$123.30
Purchase #6	$131.85	8.732%	$143.3631	$143.36	$143.35	$143.40
Purchase #7	$16.60	10.666%	$18.3706	$18.37	$18.35	$18.40
7 purchase totals =	$858.41		$928.4543	$928.44	$928.40	$928.60