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	$13.59	12.294%	$15.2608	$15.26	$15.25	$15.30
Purchase #2	$78.94	13.155%	$89.3246	$89.32	$89.30	$89.30
Purchase #3	$22.88	5.614%	$24.1645	$24.16	$24.15	$24.20
Purchase #4	$102.29	13.358%	$115.9539	$115.95	$115.95	$116.00
Purchase #5	$139.48	3.327%	$144.1205	$144.12	$144.10	$144.10
Purchase #6	$106.96	7.360%	$114.8323	$114.83	$114.85	$114.80
Purchase #7	$125.56	11.203%	$139.6265	$139.63	$139.65	$139.60
7 purchase totals =	$589.70		$643.2831	$643.27	$643.25	$643.30