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	$47.51	13.398%	$53.8754	$53.88	$53.90	$53.90
Purchase #2	$109.91	6.238%	$116.7662	$116.77	$116.75	$116.80
Purchase #3	$250.82	8.792%	$272.8721	$272.87	$272.85	$272.90
Purchase #4	$171.85	9.463%	$188.1122	$188.11	$188.10	$188.10
Purchase #5	$76.27	8.171%	$82.502	$82.50	$82.50	$82.50
Purchase #6	$61.58	8.343%	$66.7176	$66.72	$66.70	$66.70
Purchase #7	$193.44	10.396%	$213.55	$213.55	$213.55	$213.60
7 purchase totals =	$911.38		$994.3955	$994.40	$994.35	$994.50