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	$47.45	7.209%	$50.8707	$50.87	$50.85	$50.90
Purchase #2	$179.54	6.779%	$191.711	$191.71	$191.70	$191.70
Purchase #3	$81.99	9.735%	$89.9717	$89.97	$89.95	$90.00
Purchase #4	$125.81	4.350%	$131.2827	$131.28	$131.30	$131.30
Purchase #5	$40.79	10.784%	$45.1888	$45.19	$45.20	$45.20
Purchase #6	$186.72	6.565%	$198.9782	$198.98	$199.00	$199.00
Purchase #7	$249.55	12.750%	$281.3676	$281.37	$281.35	$281.40
7 purchase totals =	$911.85		$989.3707	$989.37	$989.35	$989.50