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	$55.69	5.201%	$58.5864	$58.59	$58.60	$58.60
Purchase #2	$86.27	3.572%	$89.3516	$89.35	$89.35	$89.40
Purchase #3	$86.37	12.865%	$97.4815	$97.48	$97.50	$97.50
Purchase #4	$145.64	11.204%	$161.9575	$161.96	$161.95	$162.00
Purchase #5	$127.62	4.288%	$133.0923	$133.09	$133.10	$133.10
Purchase #6	$152.72	4.498%	$159.5893	$159.59	$159.60	$159.60
Purchase #7	$109.45	9.658%	$120.0207	$120.02	$120.00	$120.00
7 purchase totals =	$763.76		$820.0793	$820.08	$820.10	$820.20