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	$83.46	6.839%	$89.1678	$89.17	$89.15	$89.20
Purchase #2	$66.94	13.614%	$76.0532	$76.05	$76.05	$76.10
Purchase #3	$101.91	3.201%	$105.1721	$105.17	$105.15	$105.20
Purchase #4	$162.91	4.870%	$170.8437	$170.84	$170.85	$170.80
Purchase #5	$134.87	13.727%	$153.3836	$153.38	$153.40	$153.40
Purchase #6	$55.45	10.813%	$61.4458	$61.45	$61.45	$61.40
Purchase #7	$150.39	10.280%	$165.8501	$165.85	$165.85	$165.90
7 purchase totals =	$755.93		$821.9163	$821.91	$821.90	$822.00