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	$234.30	12.445%	$263.4586	$263.46	$263.45	$263.50
Purchase #2	$235.34	9.107%	$256.7724	$256.77	$256.75	$256.80
Purchase #3	$112.71	9.235%	$123.1188	$123.12	$123.10	$123.10
Purchase #4	$157.39	6.653%	$167.8612	$167.86	$167.85	$167.90
Purchase #5	$233.27	12.553%	$262.5524	$262.55	$262.55	$262.60
Purchase #6	$81.35	4.621%	$85.1092	$85.11	$85.10	$85.10
Purchase #7	$55.43	5.138%	$58.278	$58.28	$58.30	$58.30
7 purchase totals =	$1,109.79		$1,217.1506	$1,217.15	$1,217.10	$1,217.30