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	$88.71	13.623%	$100.795	$100.80	$100.80	$100.80
Purchase #2	$90.41	10.453%	$99.8606	$99.86	$99.85	$99.90
Purchase #3	$198.80	10.404%	$219.4832	$219.48	$219.50	$219.50
Purchase #4	$40.70	6.377%	$43.2954	$43.30	$43.30	$43.30
Purchase #5	$41.65	9.488%	$45.6018	$45.60	$45.60	$45.60
Purchase #6	$188.98	4.313%	$197.1307	$197.13	$197.15	$197.10
Purchase #7	$113.43	10.349%	$125.1689	$125.17	$125.15	$125.20
7 purchase totals =	$762.68		$831.3356	$831.34	$831.35	$831.40