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	$123.85	4.827%	$129.8282	$129.83	$129.85	$129.80
Purchase #2	$151.64	9.363%	$165.8381	$165.84	$165.85	$165.80
Purchase #3	$27.95	5.402%	$29.4599	$29.46	$29.45	$29.50
Purchase #4	$207.89	4.797%	$217.8625	$217.86	$217.85	$217.90
Purchase #5	$6.83	12.310%	$7.6708	$7.67	$7.65	$7.70
Purchase #6	$112.68	9.841%	$123.7688	$123.77	$123.75	$123.80
Purchase #7	$18.88	10.362%	$20.8363	$20.84	$20.85	$20.80
7 purchase totals =	$649.72		$695.2646	$695.27	$695.25	$695.30