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	$5.78	8.301%	$6.2598	$6.26	$6.25	$6.30
Purchase #2	$171.31	9.636%	$187.8174	$187.82	$187.80	$187.80
Purchase #3	$119.34	13.672%	$135.6562	$135.66	$135.65	$135.70
Purchase #4	$108.75	7.429%	$116.829	$116.83	$116.85	$116.80
Purchase #5	$64.38	9.333%	$70.3886	$70.39	$70.40	$70.40
Purchase #6	$56.32	9.825%	$61.8534	$61.85	$61.85	$61.90
Purchase #7	$83.44	7.173%	$89.4252	$89.43	$89.45	$89.40
7 purchase totals =	$609.32		$668.2296	$668.24	$668.25	$668.30