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	$85.94	6.280%	$91.337	$91.34	$91.35	$91.30
Purchase #2	$79.46	4.793%	$83.2685	$83.27	$83.25	$83.30
Purchase #3	$61.32	12.159%	$68.7759	$68.78	$68.80	$68.80
Purchase #4	$14.65	6.697%	$15.6311	$15.63	$15.65	$15.60
Purchase #5	$96.78	3.757%	$100.416	$100.42	$100.40	$100.40
Purchase #6	$179.55	5.870%	$190.0896	$190.09	$190.10	$190.10
Purchase #7	$242.74	11.213%	$269.9584	$269.96	$269.95	$270.00
7 purchase totals =	$760.44		$819.4765	$819.49	$819.50	$819.50