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	$91.67	7.414%	$98.4664	$98.47	$98.45	$98.50
Purchase #2	$218.76	12.266%	$245.5931	$245.59	$245.60	$245.60
Purchase #3	$218.28	10.521%	$241.2452	$241.25	$241.25	$241.20
Purchase #4	$34.58	9.656%	$37.919	$37.92	$37.90	$37.90
Purchase #5	$165.76	7.431%	$178.0776	$178.08	$178.10	$178.10
Purchase #6	$40.73	7.687%	$43.8609	$43.86	$43.85	$43.90
Purchase #7	$41.47	7.657%	$44.6454	$44.65	$44.65	$44.60
7 purchase totals =	$811.25		$889.8076	$889.82	$889.80	$889.80