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	$123.84	11.269%	$137.7955	$137.80	$137.80	$137.80
Purchase #2	$71.82	8.443%	$77.8838	$77.88	$77.90	$77.90
Purchase #3	$179.87	5.407%	$189.5956	$189.60	$189.60	$189.60
Purchase #4	$37.86	6.822%	$40.4428	$40.44	$40.45	$40.40
Purchase #5	$107.34	4.223%	$111.873	$111.87	$111.85	$111.90
Purchase #6	$33.98	7.725%	$36.605	$36.61	$36.60	$36.60
Purchase #7	$162.54	7.834%	$175.2734	$175.27	$175.25	$175.30
7 purchase totals =	$717.25		$769.4691	$769.47	$769.45	$769.50