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	$88.49	13.530%	$100.4627	$100.46	$100.45	$100.50
Purchase #2	$174.26	8.201%	$188.5511	$188.55	$188.55	$188.60
Purchase #3	$26.72	6.648%	$28.4963	$28.50	$28.50	$28.50
Purchase #4	$166.45	8.663%	$180.8696	$180.87	$180.85	$180.90
Purchase #5	$103.43	9.114%	$112.8566	$112.86	$112.85	$112.90
Purchase #6	$68.34	10.289%	$75.3715	$75.37	$75.35	$75.40
Purchase #7	$244.30	4.146%	$254.4287	$254.43	$254.45	$254.40
7 purchase totals =	$871.99		$941.0365	$941.04	$941.00	$941.20