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	$235.64	4.556%	$246.3758	$246.38	$246.40	$246.40
Purchase #2	$123.54	7.839%	$133.2243	$133.22	$133.20	$133.20
Purchase #3	$32.98	12.671%	$37.1589	$37.16	$37.15	$37.20
Purchase #4	$222.75	13.828%	$253.5519	$253.55	$253.55	$253.60
Purchase #5	$29.72	12.456%	$33.4219	$33.42	$33.40	$33.40
Purchase #6	$47.96	13.555%	$54.461	$54.46	$54.45	$54.50
Purchase #7	$5.88	10.729%	$6.5109	$6.51	$6.50	$6.50
7 purchase totals =	$698.47		$764.7047	$764.70	$764.65	$764.80