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	$70.28	4.726%	$73.6014	$73.60	$73.60	$73.60
Purchase #2	$235.54	12.132%	$264.1157	$264.12	$264.10	$264.10
Purchase #3	$33.81	9.312%	$36.9584	$36.96	$36.95	$37.00
Purchase #4	$128.72	8.723%	$139.9482	$139.95	$139.95	$139.90
Purchase #5	$234.76	9.654%	$257.4237	$257.42	$257.40	$257.40
Purchase #6	$173.87	3.220%	$179.4686	$179.47	$179.45	$179.50
Purchase #7	$101.47	13.167%	$114.8306	$114.83	$114.85	$114.80
7 purchase totals =	$978.45		$1,066.3466	$1,066.35	$1,066.30	$1,066.30