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	$31.79	3.592%	$32.9319	$32.93	$32.95	$32.90
Purchase #2	$94.37	11.550%	$105.2697	$105.27	$105.25	$105.30
Purchase #3	$127.34	9.171%	$139.0184	$139.02	$139.00	$139.00
Purchase #4	$241.35	7.334%	$259.0506	$259.05	$259.05	$259.10
Purchase #5	$72.42	7.492%	$77.8457	$77.85	$77.85	$77.80
Purchase #6	$166.38	7.736%	$179.2512	$179.25	$179.25	$179.30
Purchase #7	$130.78	7.869%	$141.0711	$141.07	$141.05	$141.10
7 purchase totals =	$864.43		$934.4386	$934.44	$934.40	$934.50