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	$36.43	6.389%	$38.7575	$38.76	$38.75	$38.80
Purchase #2	$79.85	11.566%	$89.0855	$89.09	$89.10	$89.10
Purchase #3	$22.56	6.696%	$24.0706	$24.07	$24.05	$24.10
Purchase #4	$185.63	3.262%	$191.6853	$191.69	$191.70	$191.70
Purchase #5	$171.62	4.541%	$179.4133	$179.41	$179.40	$179.40
Purchase #6	$248.49	10.496%	$274.5715	$274.57	$274.55	$274.60
Purchase #7	$66.43	7.352%	$71.3139	$71.31	$71.30	$71.30
7 purchase totals =	$811.01		$868.8976	$868.90	$868.85	$869.00