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	$152.68	10.401%	$168.5602	$168.56	$168.55	$168.60
Purchase #2	$79.57	8.327%	$86.1958	$86.20	$86.20	$86.20
Purchase #3	$58.90	4.302%	$61.4339	$61.43	$61.45	$61.40
Purchase #4	$54.99	5.301%	$57.905	$57.91	$57.90	$57.90
Purchase #5	$92.87	7.652%	$99.9764	$99.98	$100.00	$100.00
Purchase #6	$38.79	9.626%	$42.5239	$42.52	$42.50	$42.50
Purchase #7	$250.44	8.379%	$271.4244	$271.42	$271.40	$271.40
7 purchase totals =	$728.24		$788.0196	$788.02	$788.00	$788.00