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	$35.98	11.513%	$40.1224	$40.12	$40.10	$40.10
Purchase #2	$27.51	8.723%	$29.9097	$29.91	$29.90	$29.90
Purchase #3	$66.47	4.568%	$69.5063	$69.51	$69.50	$69.50
Purchase #4	$244.41	9.413%	$267.4163	$267.42	$267.40	$267.40
Purchase #5	$128.60	5.867%	$136.145	$136.15	$136.15	$136.10
Purchase #6	$82.95	11.518%	$92.5042	$92.50	$92.50	$92.50
Purchase #7	$175.36	12.306%	$196.9398	$196.94	$196.95	$196.90
7 purchase totals =	$761.28		$832.5437	$832.55	$832.50	$832.40