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	$207.56	8.550%	$225.3064	$225.31	$225.30	$225.30
Purchase #2	$98.90	10.195%	$108.9829	$108.98	$109.00	$109.00
Purchase #3	$57.42	11.148%	$63.8212	$63.82	$63.80	$63.80
Purchase #4	$100.71	8.453%	$109.223	$109.22	$109.20	$109.20
Purchase #5	$125.44	12.542%	$141.1727	$141.17	$141.15	$141.20
Purchase #6	$93.78	13.379%	$106.3268	$106.33	$106.35	$106.30
Purchase #7	$43.30	5.830%	$45.8244	$45.82	$45.80	$45.80
7 purchase totals =	$727.11		$800.6574	$800.65	$800.60	$800.60