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	$89.98	9.868%	$98.8592	$98.86	$98.85	$98.90
Purchase #2	$90.28	12.475%	$101.5424	$101.54	$101.55	$101.50
Purchase #3	$243.61	4.687%	$255.028	$255.03	$255.05	$255.00
Purchase #4	$108.68	7.112%	$116.4093	$116.41	$116.40	$116.40
Purchase #5	$56.99	7.722%	$61.3908	$61.39	$61.40	$61.40
Purchase #6	$29.69	8.351%	$32.1694	$32.17	$32.15	$32.20
Purchase #7	$164.27	4.770%	$172.1057	$172.11	$172.10	$172.10
7 purchase totals =	$783.50		$837.5048	$837.51	$837.50	$837.50