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	$123.70	10.257%	$136.3879	$136.39	$136.40	$136.40
Purchase #2	$98.86	7.108%	$105.887	$105.89	$105.90	$105.90
Purchase #3	$99.65	3.282%	$102.9205	$102.92	$102.90	$102.90
Purchase #4	$102.46	3.217%	$105.7561	$105.76	$105.75	$105.80
Purchase #5	$101.51	11.773%	$113.4608	$113.46	$113.45	$113.50
Purchase #6	$99.78	11.156%	$110.9115	$110.91	$110.90	$110.90
Purchase #7	$42.76	6.350%	$45.4753	$45.48	$45.50	$45.50
7 purchase totals =	$668.72		$720.7991	$720.81	$720.80	$720.90