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	$41.28	3.231%	$42.6138	$42.61	$42.60	$42.60
Purchase #2	$52.40	10.827%	$58.0733	$58.07	$58.05	$58.10
Purchase #3	$79.67	13.733%	$90.6111	$90.61	$90.60	$90.60
Purchase #4	$39.69	3.667%	$41.1454	$41.15	$41.15	$41.10
Purchase #5	$104.34	6.258%	$110.8696	$110.87	$110.85	$110.90
Purchase #6	$90.92	6.558%	$96.8825	$96.88	$96.90	$96.90
Purchase #7	$154.50	10.262%	$170.3548	$170.35	$170.35	$170.40
7 purchase totals =	$562.80		$610.5505	$610.54	$610.50	$610.60