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	$76.51	9.562%	$83.8259	$83.83	$83.85	$83.80
Purchase #2	$194.99	12.271%	$218.9172	$218.92	$218.90	$218.90
Purchase #3	$23.41	9.272%	$25.5806	$25.58	$25.60	$25.60
Purchase #4	$208.86	11.770%	$233.4428	$233.44	$233.45	$233.40
Purchase #5	$231.90	8.329%	$251.215	$251.22	$251.20	$251.20
Purchase #6	$219.58	13.749%	$249.7701	$249.77	$249.75	$249.80
Purchase #7	$104.98	5.858%	$111.1297	$111.13	$111.15	$111.10
7 purchase totals =	$1,060.23		$1,173.8813	$1,173.89	$1,173.90	$1,173.80