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	$20.72	5.642%	$21.889	$21.89	$21.90	$21.90
Purchase #2	$147.88	12.544%	$166.4301	$166.43	$166.45	$166.40
Purchase #3	$83.87	11.664%	$93.6526	$93.65	$93.65	$93.70
Purchase #4	$68.43	4.609%	$71.5839	$71.58	$71.60	$71.60
Purchase #5	$116.40	9.192%	$127.0995	$127.10	$127.10	$127.10
Purchase #6	$102.85	3.354%	$106.2996	$106.30	$106.30	$106.30
Purchase #7	$18.47	10.515%	$20.4121	$20.41	$20.40	$20.40
7 purchase totals =	$558.62		$607.3668	$607.36	$607.40	$607.40