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	$44.53	5.823%	$47.123	$47.12	$47.10	$47.10
Purchase #2	$220.53	12.809%	$248.7777	$248.78	$248.80	$248.80
Purchase #3	$65.84	6.732%	$70.2723	$70.27	$70.25	$70.30
Purchase #4	$209.52	12.610%	$235.9405	$235.94	$235.95	$235.90
Purchase #5	$97.42	6.107%	$103.3694	$103.37	$103.35	$103.40
Purchase #6	$217.30	11.183%	$241.6007	$241.60	$241.60	$241.60
Purchase #7	$66.43	7.379%	$71.3319	$71.33	$71.35	$71.30
7 purchase totals =	$921.57		$1,018.4155	$1,018.41	$1,018.40	$1,018.40