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	$77.49	7.336%	$83.1747	$83.17	$83.15	$83.20
Purchase #2	$242.85	13.304%	$275.1588	$275.16	$275.15	$275.20
Purchase #3	$204.45	10.128%	$225.1567	$225.16	$225.15	$225.20
Purchase #4	$98.83	3.815%	$102.6004	$102.60	$102.60	$102.60
Purchase #5	$54.63	12.154%	$61.2697	$61.27	$61.25	$61.30
Purchase #6	$211.72	8.269%	$229.2271	$229.23	$229.25	$229.20
Purchase #7	$221.79	3.223%	$228.9383	$228.94	$228.95	$228.90
7 purchase totals =	$1,111.76		$1,205.5257	$1,205.53	$1,205.50	$1,205.60