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	$130.32	13.869%	$148.3941	$148.39	$148.40	$148.40
Purchase #2	$60.80	10.234%	$67.0223	$67.02	$67.00	$67.00
Purchase #3	$81.46	10.621%	$90.1119	$90.11	$90.10	$90.10
Purchase #4	$97.59	5.193%	$102.6578	$102.66	$102.65	$102.70
Purchase #5	$175.99	8.705%	$191.3099	$191.31	$191.30	$191.30
Purchase #6	$112.75	6.389%	$119.9536	$119.95	$119.95	$120.00
Purchase #7	$157.99	5.363%	$166.463	$166.46	$166.45	$166.50
7 purchase totals =	$816.90		$885.9126	$885.90	$885.85	$886.00