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	$42.59	7.578%	$45.8175	$45.82	$45.80	$45.80
Purchase #2	$91.86	11.565%	$102.4836	$102.48	$102.50	$102.50
Purchase #3	$93.66	7.143%	$100.3501	$100.35	$100.35	$100.40
Purchase #4	$58.69	12.354%	$65.9406	$65.94	$65.95	$65.90
Purchase #5	$180.76	7.272%	$193.9049	$193.90	$193.90	$193.90
Purchase #6	$100.75	11.105%	$111.9383	$111.94	$111.95	$111.90
Purchase #7	$47.78	13.379%	$54.1725	$54.17	$54.15	$54.20
7 purchase totals =	$616.09		$674.6075	$674.60	$674.60	$674.60