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	$77.97	9.219%	$85.1581	$85.16	$85.15	$85.20
Purchase #2	$95.29	4.206%	$99.2979	$99.30	$99.30	$99.30
Purchase #3	$181.78	8.229%	$196.7387	$196.74	$196.75	$196.70
Purchase #4	$13.77	10.375%	$15.1986	$15.20	$15.20	$15.20
Purchase #5	$65.38	4.216%	$68.1364	$68.14	$68.15	$68.10
Purchase #6	$155.64	8.345%	$168.6282	$168.63	$168.65	$168.60
Purchase #7	$122.37	7.133%	$131.0987	$131.10	$131.10	$131.10
7 purchase totals =	$712.20		$764.2566	$764.27	$764.30	$764.20