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	$78.57	5.455%	$82.856	$82.86	$82.85	$82.90
Purchase #2	$236.27	6.659%	$252.0032	$252.00	$252.00	$252.00
Purchase #3	$95.33	4.133%	$99.27	$99.27	$99.25	$99.30
Purchase #4	$76.46	6.357%	$81.3206	$81.32	$81.30	$81.30
Purchase #5	$247.64	3.200%	$255.5645	$255.56	$255.55	$255.60
Purchase #6	$67.72	13.411%	$76.8019	$76.80	$76.80	$76.80
Purchase #7	$41.62	4.180%	$43.3597	$43.36	$43.35	$43.40
7 purchase totals =	$843.61		$891.1759	$891.17	$891.10	$891.30