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	$237.98	7.307%	$255.3692	$255.37	$255.35	$255.40
Purchase #2	$39.96	12.152%	$44.8159	$44.82	$44.80	$44.80
Purchase #3	$117.58	3.768%	$122.0104	$122.01	$122.00	$122.00
Purchase #4	$69.57	12.823%	$78.491	$78.49	$78.50	$78.50
Purchase #5	$214.63	13.555%	$243.7231	$243.72	$243.70	$243.70
Purchase #6	$131.75	11.781%	$147.2715	$147.27	$147.25	$147.30
Purchase #7	$119.47	7.427%	$128.343	$128.34	$128.35	$128.30
7 purchase totals =	$930.94		$1,020.0241	$1,020.02	$1,019.95	$1,020.00