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	$23.54	9.529%	$25.7831	$25.78	$25.80	$25.80
Purchase #2	$219.64	13.270%	$248.7862	$248.79	$248.80	$248.80
Purchase #3	$238.38	10.365%	$263.0881	$263.09	$263.10	$263.10
Purchase #4	$102.32	3.166%	$105.5595	$105.56	$105.55	$105.60
Purchase #5	$133.71	6.272%	$142.0963	$142.10	$142.10	$142.10
Purchase #6	$92.55	7.773%	$99.7439	$99.74	$99.75	$99.70
Purchase #7	$237.56	8.627%	$258.0543	$258.05	$258.05	$258.10
7 purchase totals =	$1,047.70		$1,143.1114	$1,143.11	$1,143.15	$1,143.20