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	$21.40	13.858%	$24.3656	$24.37	$24.35	$24.40
Purchase #2	$165.60	8.582%	$179.8118	$179.81	$179.80	$179.80
Purchase #3	$35.32	5.594%	$37.2958	$37.30	$37.30	$37.30
Purchase #4	$127.73	13.790%	$145.344	$145.34	$145.35	$145.30
Purchase #5	$34.31	8.770%	$37.319	$37.32	$37.30	$37.30
Purchase #6	$101.52	8.690%	$110.3421	$110.34	$110.35	$110.30
Purchase #7	$235.98	12.535%	$265.5601	$265.56	$265.55	$265.60
7 purchase totals =	$721.86		$800.0384	$800.04	$800.00	$800.00