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	$25.59	7.104%	$27.4079	$27.41	$27.40	$27.40
Purchase #2	$16.55	3.309%	$17.0976	$17.10	$17.10	$17.10
Purchase #3	$67.78	13.516%	$76.9411	$76.94	$76.95	$76.90
Purchase #4	$89.50	11.522%	$99.8122	$99.81	$99.80	$99.80
Purchase #5	$149.64	8.603%	$162.5135	$162.51	$162.50	$162.50
Purchase #6	$123.94	9.255%	$135.4106	$135.41	$135.40	$135.40
Purchase #7	$112.31	9.653%	$123.1513	$123.15	$123.15	$123.20
7 purchase totals =	$585.31		$642.3342	$642.33	$642.30	$642.30