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	$9.72	12.156%	$10.9016	$10.90	$10.90	$10.90
Purchase #2	$88.57	8.729%	$96.3013	$96.30	$96.30	$96.30
Purchase #3	$196.52	8.554%	$213.3303	$213.33	$213.35	$213.30
Purchase #4	$87.60	6.559%	$93.3457	$93.35	$93.35	$93.30
Purchase #5	$106.77	5.419%	$112.5559	$112.56	$112.55	$112.60
Purchase #6	$102.32	3.511%	$105.9125	$105.91	$105.90	$105.90
Purchase #7	$72.32	12.822%	$81.5929	$81.59	$81.60	$81.60
7 purchase totals =	$663.82		$713.9402	$713.94	$713.95	$713.90