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	$81.89	10.198%	$90.2411	$90.24	$90.25	$90.20
Purchase #2	$126.35	9.579%	$138.4531	$138.45	$138.45	$138.50
Purchase #3	$82.89	10.139%	$91.2942	$91.29	$91.30	$91.30
Purchase #4	$99.58	12.584%	$112.1111	$112.11	$112.10	$112.10
Purchase #5	$215.97	10.842%	$239.3855	$239.39	$239.40	$239.40
Purchase #6	$96.40	7.164%	$103.3061	$103.31	$103.30	$103.30
Purchase #7	$243.56	13.749%	$277.0471	$277.05	$277.05	$277.00
7 purchase totals =	$946.64		$1,051.8382	$1,051.84	$1,051.85	$1,051.80