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	$66.90	6.146%	$71.0117	$71.01	$71.00	$71.00
Purchase #2	$237.56	6.495%	$252.9895	$252.99	$253.00	$253.00
Purchase #3	$85.39	4.772%	$89.4648	$89.46	$89.45	$89.50
Purchase #4	$54.45	9.361%	$59.5471	$59.55	$59.55	$59.50
Purchase #5	$125.83	6.261%	$133.7082	$133.71	$133.70	$133.70
Purchase #6	$144.88	6.234%	$153.9118	$153.91	$153.90	$153.90
Purchase #7	$51.44	4.692%	$53.8536	$53.85	$53.85	$53.90
7 purchase totals =	$766.45		$814.4867	$814.48	$814.45	$814.50