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	$88.75	9.608%	$97.2771	$97.28	$97.30	$97.30
Purchase #2	$112.75	9.621%	$123.5977	$123.60	$123.60	$123.60
Purchase #3	$186.53	10.855%	$206.7778	$206.78	$206.80	$206.80
Purchase #4	$100.34	8.740%	$109.1097	$109.11	$109.10	$109.10
Purchase #5	$174.82	12.243%	$196.2232	$196.22	$196.20	$196.20
Purchase #6	$224.89	11.456%	$250.6534	$250.65	$250.65	$250.70
Purchase #7	$99.50	6.727%	$106.1934	$106.19	$106.20	$106.20
7 purchase totals =	$987.58		$1,089.8323	$1,089.83	$1,089.85	$1,089.90