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	$132.42	8.819%	$144.0981	$144.10	$144.10	$144.10
Purchase #2	$168.43	12.840%	$190.0564	$190.06	$190.05	$190.10
Purchase #3	$223.88	5.168%	$235.4501	$235.45	$235.45	$235.50
Purchase #4	$186.92	11.831%	$209.0345	$209.03	$209.05	$209.00
Purchase #5	$19.31	8.198%	$20.893	$20.89	$20.90	$20.90
Purchase #6	$222.74	6.581%	$237.3985	$237.40	$237.40	$237.40
Purchase #7	$90.83	6.642%	$96.8629	$96.86	$96.85	$96.90
7 purchase totals =	$1,044.53		$1,133.7935	$1,133.79	$1,133.80	$1,133.90