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	$143.37	13.567%	$162.821	$162.82	$162.80	$162.80
Purchase #2	$150.83	13.279%	$170.8587	$170.86	$170.85	$170.90
Purchase #3	$100.93	6.611%	$107.6025	$107.60	$107.60	$107.60
Purchase #4	$68.94	13.430%	$78.1986	$78.20	$78.20	$78.20
Purchase #5	$43.57	6.362%	$46.3419	$46.34	$46.35	$46.30
Purchase #6	$179.45	13.526%	$203.7224	$203.72	$203.70	$203.70
Purchase #7	$43.63	3.612%	$45.2059	$45.21	$45.20	$45.20
7 purchase totals =	$730.72		$814.7510	$814.75	$814.70	$814.70