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	$147.34	12.346%	$165.5306	$165.53	$165.55	$165.50
Purchase #2	$40.71	6.197%	$43.2328	$43.23	$43.25	$43.20
Purchase #3	$17.52	13.446%	$19.8757	$19.88	$19.90	$19.90
Purchase #4	$238.66	6.740%	$254.7457	$254.75	$254.75	$254.70
Purchase #5	$214.57	13.810%	$244.2021	$244.20	$244.20	$244.20
Purchase #6	$57.89	11.173%	$64.358	$64.36	$64.35	$64.40
Purchase #7	$98.34	13.651%	$111.7644	$111.76	$111.75	$111.80
7 purchase totals =	$815.03		$903.7093	$903.71	$903.75	$903.70