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	$239.87	4.275%	$250.1244	$250.12	$250.10	$250.10
Purchase #2	$250.80	8.105%	$271.1273	$271.13	$271.15	$271.10
Purchase #3	$88.62	12.860%	$100.0165	$100.02	$100.00	$100.00
Purchase #4	$180.43	13.747%	$205.2337	$205.23	$205.25	$205.20
Purchase #5	$104.53	9.180%	$114.1259	$114.13	$114.15	$114.10
Purchase #6	$89.73	9.757%	$98.485	$98.49	$98.50	$98.50
Purchase #7	$77.98	13.857%	$88.7857	$88.79	$88.80	$88.80
7 purchase totals =	$1,031.96		$1,127.8985	$1,127.91	$1,127.95	$1,127.80