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	$29.59	11.232%	$32.9135	$32.91	$32.90	$32.90
Purchase #2	$32.38	9.114%	$35.3311	$35.33	$35.35	$35.30
Purchase #3	$67.97	4.317%	$70.9043	$70.90	$70.90	$70.90
Purchase #4	$38.35	7.450%	$41.2071	$41.21	$41.20	$41.20
Purchase #5	$134.43	12.672%	$151.465	$151.47	$151.45	$151.50
Purchase #6	$153.43	13.150%	$173.606	$173.61	$173.60	$173.60
Purchase #7	$249.88	7.432%	$268.4511	$268.45	$268.45	$268.50
7 purchase totals =	$706.03		$773.8781	$773.88	$773.85	$773.90