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	$82.80	6.695%	$88.3435	$88.34	$88.35	$88.30
Purchase #2	$103.27	4.659%	$108.0813	$108.08	$108.10	$108.10
Purchase #3	$127.35	9.368%	$139.2801	$139.28	$139.30	$139.30
Purchase #4	$223.71	3.439%	$231.4034	$231.40	$231.40	$231.40
Purchase #5	$204.53	9.320%	$223.5922	$223.59	$223.60	$223.60
Purchase #6	$120.61	11.364%	$134.3161	$134.32	$134.30	$134.30
Purchase #7	$103.85	7.124%	$111.2483	$111.25	$111.25	$111.20
7 purchase totals =	$966.12		$1,036.2649	$1,036.26	$1,036.30	$1,036.20