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	$141.89	10.652%	$157.0041	$157.00	$157.00	$157.00
Purchase #2	$80.53	12.624%	$90.6961	$90.70	$90.70	$90.70
Purchase #3	$188.34	11.352%	$209.7204	$209.72	$209.70	$209.70
Purchase #4	$65.50	11.197%	$72.834	$72.83	$72.85	$72.80
Purchase #5	$48.50	12.491%	$54.5581	$54.56	$54.55	$54.60
Purchase #6	$104.38	12.518%	$117.4463	$117.45	$117.45	$117.40
Purchase #7	$71.98	10.201%	$79.3227	$79.32	$79.30	$79.30
7 purchase totals =	$701.12		$781.5817	$781.58	$781.55	$781.50