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	$48.50	9.729%	$53.2186	$53.22	$53.20	$53.20
Purchase #2	$129.76	8.665%	$141.0037	$141.00	$141.00	$141.00
Purchase #3	$37.79	5.410%	$39.8344	$39.83	$39.85	$39.80
Purchase #4	$67.95	7.160%	$72.8152	$72.82	$72.80	$72.80
Purchase #5	$100.44	12.341%	$112.8353	$112.84	$112.85	$112.80
Purchase #6	$213.54	5.467%	$225.2142	$225.21	$225.20	$225.20
Purchase #7	$168.87	3.399%	$174.6099	$174.61	$174.60	$174.60
7 purchase totals =	$766.85		$819.5313	$819.53	$819.50	$819.40