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	$60.30	11.776%	$67.4009	$67.40	$67.40	$67.40
Purchase #2	$37.66	7.386%	$40.4416	$40.44	$40.45	$40.40
Purchase #3	$118.41	7.512%	$127.305	$127.31	$127.30	$127.30
Purchase #4	$176.94	7.810%	$190.759	$190.76	$190.75	$190.80
Purchase #5	$202.46	6.164%	$214.9396	$214.94	$214.95	$214.90
Purchase #6	$155.30	9.331%	$169.791	$169.79	$169.80	$169.80
Purchase #7	$81.94	10.776%	$90.7699	$90.77	$90.75	$90.80
7 purchase totals =	$833.01		$901.4070	$901.41	$901.40	$901.40