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	$51.98	13.746%	$59.1252	$59.13	$59.15	$59.10
Purchase #2	$145.88	11.439%	$162.5672	$162.57	$162.55	$162.60
Purchase #3	$140.77	7.759%	$151.6923	$151.69	$151.70	$151.70
Purchase #4	$86.82	8.663%	$94.3412	$94.34	$94.35	$94.30
Purchase #5	$104.27	7.490%	$112.0798	$112.08	$112.10	$112.10
Purchase #6	$84.47	9.250%	$92.2835	$92.28	$92.30	$92.30
Purchase #7	$162.82	7.788%	$175.5004	$175.50	$175.50	$175.50
7 purchase totals =	$777.01		$847.5896	$847.59	$847.65	$847.60