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	$36.51	6.279%	$38.8025	$38.80	$38.80	$38.80
Purchase #2	$133.96	11.332%	$149.1403	$149.14	$149.15	$149.10
Purchase #3	$96.77	12.810%	$109.1662	$109.17	$109.15	$109.20
Purchase #4	$55.85	9.507%	$61.1597	$61.16	$61.15	$61.20
Purchase #5	$99.47	12.567%	$111.9704	$111.97	$111.95	$112.00
Purchase #6	$231.58	7.394%	$248.703	$248.70	$248.70	$248.70
Purchase #7	$167.79	10.609%	$185.5908	$185.59	$185.60	$185.60
7 purchase totals =	$821.93		$904.5329	$904.53	$904.50	$904.60