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	$143.29	10.344%	$158.1119	$158.11	$158.10	$158.10
Purchase #2	$115.63	6.786%	$123.4767	$123.48	$123.50	$123.50
Purchase #3	$92.74	13.268%	$105.0447	$105.04	$105.05	$105.00
Purchase #4	$96.57	12.108%	$108.2627	$108.26	$108.25	$108.30
Purchase #5	$145.33	3.591%	$150.5488	$150.55	$150.55	$150.50
Purchase #6	$77.47	4.740%	$81.1421	$81.14	$81.15	$81.10
Purchase #7	$233.87	10.773%	$259.0648	$259.06	$259.05	$259.10
7 purchase totals =	$904.90		$985.6517	$985.64	$985.65	$985.60