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	$205.73	7.645%	$221.4581	$221.46	$221.45	$221.50
Purchase #2	$100.42	8.693%	$109.1495	$109.15	$109.15	$109.10
Purchase #3	$248.90	9.610%	$272.8193	$272.82	$272.80	$272.80
Purchase #4	$40.39	12.848%	$45.5793	$45.58	$45.60	$45.60
Purchase #5	$221.96	3.589%	$229.9261	$229.93	$229.95	$229.90
Purchase #6	$33.84	11.668%	$37.7885	$37.79	$37.80	$37.80
Purchase #7	$18.94	6.386%	$20.1495	$20.15	$20.15	$20.10
7 purchase totals =	$870.18		$936.8703	$936.88	$936.90	$936.80