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	$137.40	5.478%	$144.9268	$144.93	$144.95	$144.90
Purchase #2	$207.32	7.417%	$222.6969	$222.70	$222.70	$222.70
Purchase #3	$238.52	4.646%	$249.6016	$249.60	$249.60	$249.60
Purchase #4	$37.79	8.162%	$40.8744	$40.87	$40.85	$40.90
Purchase #5	$108.35	8.478%	$117.5359	$117.54	$117.55	$117.50
Purchase #6	$250.83	11.694%	$280.1621	$280.16	$280.15	$280.20
Purchase #7	$209.89	9.465%	$229.7561	$229.76	$229.75	$229.80
7 purchase totals =	$1,190.10		$1,285.5538	$1,285.56	$1,285.55	$1,285.60