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	$18.44	4.782%	$19.3218	$19.32	$19.30	$19.30
Purchase #2	$184.59	13.786%	$210.0376	$210.04	$210.05	$210.00
Purchase #3	$170.39	9.783%	$187.0593	$187.06	$187.05	$187.10
Purchase #4	$77.59	13.759%	$88.2656	$88.27	$88.25	$88.30
Purchase #5	$59.68	13.330%	$67.6353	$67.64	$67.65	$67.60
Purchase #6	$104.50	4.648%	$109.3572	$109.36	$109.35	$109.40
Purchase #7	$39.77	4.198%	$41.4395	$41.44	$41.45	$41.40
7 purchase totals =	$654.96		$723.1163	$723.13	$723.10	$723.10