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	$79.40	8.171%	$85.8878	$85.89	$85.90	$85.90
Purchase #2	$133.56	4.715%	$139.8574	$139.86	$139.85	$139.90
Purchase #3	$16.76	10.159%	$18.4626	$18.46	$18.45	$18.50
Purchase #4	$181.93	10.111%	$200.3249	$200.32	$200.30	$200.30
Purchase #5	$20.97	7.206%	$22.4811	$22.48	$22.50	$22.50
Purchase #6	$25.28	11.506%	$28.1887	$28.19	$28.20	$28.20
Purchase #7	$39.56	13.322%	$44.8302	$44.83	$44.85	$44.80
7 purchase totals =	$497.46		$540.0327	$540.03	$540.05	$540.10