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	$44.86	11.188%	$49.8789	$49.88	$49.90	$49.90
Purchase #2	$246.63	11.619%	$275.2859	$275.29	$275.30	$275.30
Purchase #3	$196.33	9.649%	$215.2739	$215.27	$215.25	$215.30
Purchase #4	$115.32	9.176%	$125.9018	$125.90	$125.90	$125.90
Purchase #5	$30.60	4.399%	$31.9461	$31.95	$31.95	$31.90
Purchase #6	$73.72	5.374%	$77.6817	$77.68	$77.70	$77.70
Purchase #7	$212.52	6.296%	$225.9003	$225.90	$225.90	$225.90
7 purchase totals =	$919.98		$1,001.8686	$1,001.87	$1,001.90	$1,001.90