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	$73.42	9.806%	$80.6196	$80.62	$80.60	$80.60
Purchase #2	$240.67	7.806%	$259.4567	$259.46	$259.45	$259.50
Purchase #3	$24.90	9.778%	$27.3347	$27.33	$27.35	$27.30
Purchase #4	$39.62	4.270%	$41.3118	$41.31	$41.30	$41.30
Purchase #5	$50.68	11.569%	$56.5432	$56.54	$56.55	$56.50
Purchase #6	$118.44	10.742%	$131.1628	$131.16	$131.15	$131.20
Purchase #7	$25.47	12.364%	$28.6191	$28.62	$28.60	$28.60
7 purchase totals =	$573.20		$625.0479	$625.04	$625.00	$625.00