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	$149.85	12.461%	$168.5228	$168.52	$168.50	$168.50
Purchase #2	$17.31	3.693%	$17.9493	$17.95	$17.95	$17.90
Purchase #3	$35.47	12.578%	$39.9314	$39.93	$39.95	$39.90
Purchase #4	$43.69	3.308%	$45.1353	$45.14	$45.15	$45.10
Purchase #5	$237.46	12.658%	$267.5177	$267.52	$267.50	$267.50
Purchase #6	$6.71	11.791%	$7.5012	$7.50	$7.50	$7.50
Purchase #7	$112.35	12.851%	$126.7881	$126.79	$126.80	$126.80
7 purchase totals =	$602.84		$673.3458	$673.35	$673.35	$673.20