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	$84.53	6.405%	$89.9441	$89.94	$89.95	$89.90
Purchase #2	$224.31	11.359%	$249.7894	$249.79	$249.80	$249.80
Purchase #3	$32.68	13.346%	$37.0415	$37.04	$37.05	$37.00
Purchase #4	$211.47	10.448%	$233.5644	$233.56	$233.55	$233.60
Purchase #5	$123.73	3.651%	$128.2474	$128.25	$128.25	$128.20
Purchase #6	$57.25	12.237%	$64.2557	$64.26	$64.25	$64.30
Purchase #7	$186.89	5.404%	$196.9895	$196.99	$197.00	$197.00
7 purchase totals =	$920.86		$999.8320	$999.83	$999.85	$999.80