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	$79.27	13.503%	$89.9738	$89.97	$89.95	$90.00
Purchase #2	$11.45	3.246%	$11.8217	$11.82	$11.80	$11.80
Purchase #3	$152.76	6.740%	$163.056	$163.06	$163.05	$163.10
Purchase #4	$153.33	8.854%	$166.9058	$166.91	$166.90	$166.90
Purchase #5	$77.62	6.490%	$82.6575	$82.66	$82.65	$82.70
Purchase #6	$109.61	12.220%	$123.0043	$123.00	$123.00	$123.00
Purchase #7	$128.73	10.505%	$142.2531	$142.25	$142.25	$142.30
7 purchase totals =	$712.77		$779.6722	$779.67	$779.60	$779.80