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	$90.97	5.639%	$96.0998	$96.10	$96.10	$96.10
Purchase #2	$192.83	13.845%	$219.5273	$219.53	$219.55	$219.50
Purchase #3	$135.60	5.543%	$143.1163	$143.12	$143.10	$143.10
Purchase #4	$241.66	5.403%	$254.7169	$254.72	$254.70	$254.70
Purchase #5	$240.26	13.789%	$273.3895	$273.39	$273.40	$273.40
Purchase #6	$53.82	13.798%	$61.2461	$61.25	$61.25	$61.20
Purchase #7	$28.88	11.553%	$32.2165	$32.22	$32.20	$32.20
7 purchase totals =	$984.02		$1,080.3124	$1,080.33	$1,080.30	$1,080.20