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	$126.47	13.273%	$143.2564	$143.26	$143.25	$143.30
Purchase #2	$181.49	4.625%	$189.8839	$189.88	$189.90	$189.90
Purchase #3	$89.48	6.523%	$95.3168	$95.32	$95.30	$95.30
Purchase #4	$91.66	8.693%	$99.628	$99.63	$99.65	$99.60
Purchase #5	$5.82	7.549%	$6.2594	$6.26	$6.25	$6.30
Purchase #6	$128.94	11.614%	$143.9151	$143.92	$143.90	$143.90
Purchase #7	$156.45	5.617%	$165.2378	$165.24	$165.25	$165.20
7 purchase totals =	$780.31		$843.4974	$843.51	$843.50	$843.50