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	$78.65	6.315%	$83.6167	$83.62	$83.60	$83.60
Purchase #2	$126.69	13.824%	$144.2036	$144.20	$144.20	$144.20
Purchase #3	$163.37	6.587%	$174.1312	$174.13	$174.15	$174.10
Purchase #4	$109.63	12.668%	$123.5179	$123.52	$123.50	$123.50
Purchase #5	$87.56	3.702%	$90.8015	$90.80	$90.80	$90.80
Purchase #6	$81.52	5.688%	$86.1569	$86.16	$86.15	$86.20
Purchase #7	$59.88	13.544%	$67.9901	$67.99	$68.00	$68.00
7 purchase totals =	$707.30		$770.4179	$770.42	$770.40	$770.40