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	$36.58	4.722%	$38.3073	$38.31	$38.30	$38.30
Purchase #2	$171.60	5.536%	$181.0998	$181.10	$181.10	$181.10
Purchase #3	$159.78	7.125%	$171.1643	$171.16	$171.15	$171.20
Purchase #4	$148.26	13.557%	$168.3596	$168.36	$168.35	$168.40
Purchase #5	$206.31	6.254%	$219.2126	$219.21	$219.20	$219.20
Purchase #6	$167.57	6.312%	$178.147	$178.15	$178.15	$178.10
Purchase #7	$57.36	8.636%	$62.3136	$62.31	$62.30	$62.30
7 purchase totals =	$947.46		$1,018.6042	$1,018.60	$1,018.55	$1,018.60