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	$19.27	9.751%	$21.149	$21.15	$21.15	$21.10
Purchase #2	$45.94	11.619%	$51.2778	$51.28	$51.30	$51.30
Purchase #3	$92.70	5.564%	$97.8578	$97.86	$97.85	$97.90
Purchase #4	$124.40	10.251%	$137.1522	$137.15	$137.15	$137.20
Purchase #5	$179.52	9.299%	$196.2136	$196.21	$196.20	$196.20
Purchase #6	$87.94	7.315%	$94.3728	$94.37	$94.35	$94.40
Purchase #7	$13.30	11.645%	$14.8488	$14.85	$14.85	$14.80
7 purchase totals =	$563.07		$612.8720	$612.87	$612.85	$612.90