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	$127.54	9.657%	$139.8565	$139.86	$139.85	$139.90
Purchase #2	$39.41	7.796%	$42.4824	$42.48	$42.50	$42.50
Purchase #3	$51.69	5.438%	$54.5009	$54.50	$54.50	$54.50
Purchase #4	$76.67	8.712%	$83.3495	$83.35	$83.35	$83.30
Purchase #5	$110.74	10.580%	$122.4563	$122.46	$122.45	$122.50
Purchase #6	$83.27	10.212%	$91.7735	$91.77	$91.75	$91.80
Purchase #7	$65.52	5.616%	$69.1996	$69.20	$69.20	$69.20
7 purchase totals =	$554.84		$603.6187	$603.62	$603.60	$603.70