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	$51.51	12.797%	$58.1017	$58.10	$58.10	$58.10
Purchase #2	$189.82	11.613%	$211.8638	$211.86	$211.85	$211.90
Purchase #3	$30.52	12.744%	$34.4095	$34.41	$34.40	$34.40
Purchase #4	$193.59	4.774%	$202.832	$202.83	$202.85	$202.80
Purchase #5	$82.91	3.291%	$85.6386	$85.64	$85.65	$85.60
Purchase #6	$95.90	10.366%	$105.841	$105.84	$105.85	$105.80
Purchase #7	$82.46	3.581%	$85.4129	$85.41	$85.40	$85.40
7 purchase totals =	$726.71		$784.0995	$784.09	$784.10	$784.00