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	$6.84	12.115%	$7.6687	$7.67	$7.65	$7.70
Purchase #2	$108.65	13.602%	$123.4286	$123.43	$123.45	$123.40
Purchase #3	$14.94	6.297%	$15.8808	$15.88	$15.90	$15.90
Purchase #4	$90.75	9.792%	$99.6362	$99.64	$99.65	$99.60
Purchase #5	$7.98	11.266%	$8.879	$8.88	$8.90	$8.90
Purchase #6	$63.93	13.278%	$72.4186	$72.42	$72.40	$72.40
Purchase #7	$194.96	10.400%	$215.2358	$215.24	$215.25	$215.20
7 purchase totals =	$488.05		$543.1477	$543.16	$543.20	$543.10