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	$165.53	5.619%	$174.8311	$174.83	$174.85	$174.80
Purchase #2	$70.95	10.531%	$78.4217	$78.42	$78.40	$78.40
Purchase #3	$16.52	10.729%	$18.2924	$18.29	$18.30	$18.30
Purchase #4	$123.75	13.488%	$140.4414	$140.44	$140.45	$140.40
Purchase #5	$86.96	4.381%	$90.7697	$90.77	$90.75	$90.80
Purchase #6	$126.27	3.238%	$130.3586	$130.36	$130.35	$130.40
Purchase #7	$212.28	4.192%	$221.1788	$221.18	$221.20	$221.20
7 purchase totals =	$802.26		$854.2937	$854.29	$854.30	$854.30