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	$71.74	9.760%	$78.7418	$78.74	$78.75	$78.70
Purchase #2	$153.83	12.113%	$172.4634	$172.46	$172.45	$172.50
Purchase #3	$94.90	5.317%	$99.9458	$99.95	$99.95	$99.90
Purchase #4	$46.32	4.211%	$48.2705	$48.27	$48.25	$48.30
Purchase #5	$73.55	3.303%	$75.9794	$75.98	$76.00	$76.00
Purchase #6	$198.76	10.773%	$220.1724	$220.17	$220.15	$220.20
Purchase #7	$196.31	3.411%	$203.0061	$203.01	$203.00	$203.00
7 purchase totals =	$835.41		$898.5794	$898.58	$898.55	$898.60