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	$36.58	11.694%	$40.8577	$40.86	$40.85	$40.90
Purchase #2	$149.93	13.617%	$170.346	$170.35	$170.35	$170.30
Purchase #3	$46.42	3.824%	$48.1951	$48.20	$48.20	$48.20
Purchase #4	$116.34	3.216%	$120.0815	$120.08	$120.10	$120.10
Purchase #5	$67.73	7.197%	$72.6045	$72.60	$72.60	$72.60
Purchase #6	$77.44	6.706%	$82.6331	$82.63	$82.65	$82.60
Purchase #7	$123.54	4.218%	$128.7509	$128.75	$128.75	$128.80
7 purchase totals =	$617.98		$663.4688	$663.47	$663.50	$663.50