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	$92.98	8.534%	$100.9149	$100.91	$100.90	$100.90
Purchase #2	$180.54	4.619%	$188.8791	$188.88	$188.90	$188.90
Purchase #3	$228.63	5.714%	$241.6939	$241.69	$241.70	$241.70
Purchase #4	$100.59	5.256%	$105.877	$105.88	$105.90	$105.90
Purchase #5	$37.64	4.356%	$39.2796	$39.28	$39.30	$39.30
Purchase #6	$101.79	9.207%	$111.1618	$111.16	$111.15	$111.20
Purchase #7	$130.30	7.660%	$140.281	$140.28	$140.30	$140.30
7 purchase totals =	$872.47		$928.0873	$928.08	$928.15	$928.20