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	$86.62	5.121%	$91.0558	$91.06	$91.05	$91.10
Purchase #2	$39.26	8.110%	$42.444	$42.44	$42.45	$42.40
Purchase #3	$85.79	6.382%	$91.2651	$91.27	$91.25	$91.30
Purchase #4	$81.98	4.217%	$85.4371	$85.44	$85.45	$85.40
Purchase #5	$20.28	10.354%	$22.3798	$22.38	$22.40	$22.40
Purchase #6	$198.54	12.179%	$222.7202	$222.72	$222.70	$222.70
Purchase #7	$16.51	7.602%	$17.7651	$17.77	$17.75	$17.80
7 purchase totals =	$528.98		$573.0671	$573.08	$573.05	$573.10