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	$83.33	7.829%	$89.8539	$89.85	$89.85	$89.90
Purchase #2	$105.64	3.643%	$109.4885	$109.49	$109.50	$109.50
Purchase #3	$29.37	10.218%	$32.371	$32.37	$32.35	$32.40
Purchase #4	$231.31	12.336%	$259.8444	$259.84	$259.85	$259.80
Purchase #5	$185.30	12.338%	$208.1623	$208.16	$208.15	$208.20
Purchase #6	$23.56	6.177%	$25.0153	$25.02	$25.00	$25.00
Purchase #7	$19.38	11.652%	$21.6382	$21.64	$21.65	$21.60
7 purchase totals =	$677.89		$746.3736	$746.37	$746.35	$746.40