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	$128.95	6.221%	$136.972	$136.97	$136.95	$137.00
Purchase #2	$39.90	10.143%	$43.9471	$43.95	$43.95	$43.90
Purchase #3	$160.74	11.586%	$179.3633	$179.36	$179.35	$179.40
Purchase #4	$55.69	6.348%	$59.2252	$59.23	$59.25	$59.20
Purchase #5	$123.45	12.103%	$138.3912	$138.39	$138.40	$138.40
Purchase #6	$20.44	3.543%	$21.1642	$21.16	$21.15	$21.20
Purchase #7	$228.44	4.366%	$238.4137	$238.41	$238.40	$238.40
7 purchase totals =	$757.61		$817.4767	$817.47	$817.45	$817.50