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	$180.29	4.782%	$188.9115	$188.91	$188.90	$188.90
Purchase #2	$75.42	9.294%	$82.4295	$82.43	$82.45	$82.40
Purchase #3	$83.91	8.560%	$91.0927	$91.09	$91.10	$91.10
Purchase #4	$39.51	4.478%	$41.2793	$41.28	$41.30	$41.30
Purchase #5	$203.45	5.859%	$215.3701	$215.37	$215.35	$215.40
Purchase #6	$237.77	4.350%	$248.113	$248.11	$248.10	$248.10
Purchase #7	$29.49	12.764%	$33.2541	$33.25	$33.25	$33.30
7 purchase totals =	$849.84		$900.4502	$900.44	$900.45	$900.50