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	$50.50	7.128%	$54.0996	$54.10	$54.10	$54.10
Purchase #2	$11.89	10.497%	$13.1381	$13.14	$13.15	$13.10
Purchase #3	$105.48	6.115%	$111.9301	$111.93	$111.95	$111.90
Purchase #4	$12.91	7.751%	$13.9107	$13.91	$13.90	$13.90
Purchase #5	$87.86	11.668%	$98.1115	$98.11	$98.10	$98.10
Purchase #6	$21.92	7.345%	$23.53	$23.53	$23.55	$23.50
Purchase #7	$73.81	4.853%	$77.392	$77.39	$77.40	$77.40
7 purchase totals =	$364.37		$392.1120	$392.11	$392.15	$392.00