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	$140.29	4.643%	$146.8037	$146.80	$146.80	$146.80
Purchase #2	$118.53	10.635%	$131.1357	$131.14	$131.15	$131.10
Purchase #3	$202.70	7.734%	$218.3768	$218.38	$218.40	$218.40
Purchase #4	$152.37	4.874%	$159.7965	$159.80	$159.80	$159.80
Purchase #5	$169.43	7.374%	$181.9238	$181.92	$181.90	$181.90
Purchase #6	$134.99	7.114%	$144.5932	$144.59	$144.60	$144.60
Purchase #7	$20.54	3.835%	$21.3277	$21.33	$21.35	$21.30
7 purchase totals =	$938.85		$1,003.9574	$1,003.96	$1,004.00	$1,003.90