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	$63.94	9.599%	$70.0776	$70.08	$70.10	$70.10
Purchase #2	$53.37	4.105%	$55.5608	$55.56	$55.55	$55.60
Purchase #3	$45.76	8.401%	$49.6043	$49.60	$49.60	$49.60
Purchase #4	$56.50	8.475%	$61.2884	$61.29	$61.30	$61.30
Purchase #5	$82.63	4.714%	$86.5252	$86.53	$86.55	$86.50
Purchase #6	$93.82	5.610%	$99.0833	$99.08	$99.10	$99.10
Purchase #7	$146.77	3.699%	$152.199	$152.20	$152.20	$152.20
7 purchase totals =	$542.79		$574.3386	$574.34	$574.40	$574.40