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	$18.71	10.708%	$20.7135	$20.71	$20.70	$20.70
Purchase #2	$223.38	4.428%	$233.2713	$233.27	$233.25	$233.30
Purchase #3	$226.62	7.613%	$243.8726	$243.87	$243.85	$243.90
Purchase #4	$130.97	5.319%	$137.9363	$137.94	$137.95	$137.90
Purchase #5	$54.63	8.789%	$59.4314	$59.43	$59.45	$59.40
Purchase #6	$222.33	8.837%	$241.9773	$241.98	$242.00	$242.00
Purchase #7	$45.85	12.455%	$51.5606	$51.56	$51.55	$51.60
7 purchase totals =	$922.49		$988.7630	$988.76	$988.75	$988.80