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	$99.60	5.746%	$105.323	$105.32	$105.30	$105.30
Purchase #2	$148.71	12.469%	$167.2526	$167.25	$167.25	$167.30
Purchase #3	$118.50	4.460%	$123.7851	$123.79	$123.80	$123.80
Purchase #4	$106.83	11.501%	$119.1165	$119.12	$119.10	$119.10
Purchase #5	$66.31	7.399%	$71.2163	$71.22	$71.20	$71.20
Purchase #6	$103.54	9.647%	$113.5285	$113.53	$113.55	$113.50
Purchase #7	$34.81	11.674%	$38.8737	$38.87	$38.85	$38.90
7 purchase totals =	$678.30		$739.0957	$739.10	$739.05	$739.10