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	$227.56	12.243%	$255.4202	$255.42	$255.40	$255.40
Purchase #2	$54.92	12.368%	$61.7125	$61.71	$61.70	$61.70
Purchase #3	$140.98	6.671%	$150.3848	$150.38	$150.40	$150.40
Purchase #4	$216.90	5.775%	$229.426	$229.43	$229.45	$229.40
Purchase #5	$220.95	7.830%	$238.2504	$238.25	$238.25	$238.30
Purchase #6	$37.67	10.410%	$41.5914	$41.59	$41.60	$41.60
Purchase #7	$79.72	6.344%	$84.7774	$84.78	$84.80	$84.80
7 purchase totals =	$978.70		$1,061.5627	$1,061.56	$1,061.60	$1,061.60