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	$117.40	11.830%	$131.2884	$131.29	$131.30	$131.30
Purchase #2	$139.60	4.326%	$145.6391	$145.64	$145.65	$145.60
Purchase #3	$103.75	5.614%	$109.5745	$109.57	$109.55	$109.60
Purchase #4	$19.64	3.267%	$20.2816	$20.28	$20.30	$20.30
Purchase #5	$80.78	11.830%	$90.3363	$90.34	$90.35	$90.30
Purchase #6	$42.57	4.107%	$44.3183	$44.32	$44.30	$44.30
Purchase #7	$123.41	9.435%	$135.0537	$135.05	$135.05	$135.10
7 purchase totals =	$627.15		$676.4919	$676.49	$676.50	$676.50