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	$11.25	6.295%	$11.9582	$11.96	$11.95	$12.00
Purchase #2	$154.75	7.266%	$165.9941	$165.99	$166.00	$166.00
Purchase #3	$95.32	4.728%	$99.8267	$99.83	$99.85	$99.80
Purchase #4	$233.27	7.182%	$250.0235	$250.02	$250.00	$250.00
Purchase #5	$68.47	5.830%	$72.4618	$72.46	$72.45	$72.50
Purchase #6	$120.94	10.495%	$133.6327	$133.63	$133.65	$133.60
Purchase #7	$122.48	7.407%	$131.5521	$131.55	$131.55	$131.60
7 purchase totals =	$806.48		$865.4491	$865.44	$865.45	$865.50