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	$30.64	10.443%	$33.8397	$33.84	$33.85	$33.80
Purchase #2	$132.38	11.626%	$147.7705	$147.77	$147.75	$147.80
Purchase #3	$92.97	11.407%	$103.5751	$103.58	$103.60	$103.60
Purchase #4	$90.68	9.753%	$99.524	$99.52	$99.50	$99.50
Purchase #5	$134.56	4.220%	$140.2384	$140.24	$140.25	$140.20
Purchase #6	$205.91	3.752%	$213.6357	$213.64	$213.65	$213.60
Purchase #7	$180.87	4.671%	$189.3184	$189.32	$189.30	$189.30
7 purchase totals =	$868.01		$927.9018	$927.91	$927.90	$927.80