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	$50.33	5.756%	$53.227	$53.23	$53.25	$53.20
Purchase #2	$115.73	12.836%	$130.5851	$130.59	$130.60	$130.60
Purchase #3	$117.58	7.590%	$126.5043	$126.50	$126.50	$126.50
Purchase #4	$174.66	8.723%	$189.8956	$189.90	$189.90	$189.90
Purchase #5	$34.39	10.622%	$38.0429	$38.04	$38.05	$38.00
Purchase #6	$197.42	13.116%	$223.3136	$223.31	$223.30	$223.30
Purchase #7	$248.38	4.200%	$258.812	$258.81	$258.80	$258.80
7 purchase totals =	$938.49		$1,020.3805	$1,020.38	$1,020.40	$1,020.30