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	$207.69	5.728%	$219.5865	$219.59	$219.60	$219.60
Purchase #2	$240.47	7.679%	$258.9357	$258.94	$258.95	$258.90
Purchase #3	$215.72	12.866%	$243.4745	$243.47	$243.45	$243.50
Purchase #4	$203.73	9.345%	$222.7686	$222.77	$222.75	$222.80
Purchase #5	$115.75	12.643%	$130.3843	$130.38	$130.40	$130.40
Purchase #6	$7.79	6.683%	$8.3106	$8.31	$8.30	$8.30
Purchase #7	$228.59	9.404%	$250.0866	$250.09	$250.10	$250.10
7 purchase totals =	$1,219.74		$1,333.5468	$1,333.55	$1,333.55	$1,333.60