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	$152.62	12.321%	$171.4243	$171.42	$171.40	$171.40
Purchase #2	$164.53	12.814%	$185.6129	$185.61	$185.60	$185.60
Purchase #3	$132.51	12.430%	$148.981	$148.98	$149.00	$149.00
Purchase #4	$57.63	6.804%	$61.5511	$61.55	$61.55	$61.60
Purchase #5	$22.53	13.628%	$25.6004	$25.60	$25.60	$25.60
Purchase #6	$211.76	5.178%	$222.7249	$222.72	$222.70	$222.70
Purchase #7	$74.32	10.507%	$82.1288	$82.13	$82.15	$82.10
7 purchase totals =	$815.90		$898.0234	$898.01	$898.00	$898.00