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	$38.47	9.619%	$42.1704	$42.17	$42.15	$42.20
Purchase #2	$48.76	11.502%	$54.3684	$54.37	$54.35	$54.40
Purchase #3	$103.43	6.524%	$110.1778	$110.18	$110.20	$110.20
Purchase #4	$171.31	9.259%	$187.1716	$187.17	$187.15	$187.20
Purchase #5	$49.98	5.674%	$52.8159	$52.82	$52.80	$52.80
Purchase #6	$172.41	4.846%	$180.765	$180.77	$180.75	$180.80
Purchase #7	$232.26	10.390%	$256.3918	$256.39	$256.40	$256.40
7 purchase totals =	$816.62		$883.8609	$883.87	$883.80	$884.00