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	$101.68	4.172%	$105.9221	$105.92	$105.90	$105.90
Purchase #2	$101.68	13.516%	$115.4231	$115.42	$115.40	$115.40
Purchase #3	$82.93	4.641%	$86.7788	$86.78	$86.80	$86.80
Purchase #4	$80.28	10.358%	$88.5954	$88.60	$88.60	$88.60
Purchase #5	$181.87	5.851%	$192.5112	$192.51	$192.50	$192.50
Purchase #6	$160.66	11.735%	$179.5135	$179.51	$179.50	$179.50
Purchase #7	$61.42	10.306%	$67.7499	$67.75	$67.75	$67.70
7 purchase totals =	$770.52		$836.4940	$836.49	$836.45	$836.40