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	$30.63	8.834%	$33.3359	$33.34	$33.35	$33.30
Purchase #2	$170.64	13.777%	$194.1491	$194.15	$194.15	$194.10
Purchase #3	$17.60	4.523%	$18.396	$18.40	$18.40	$18.40
Purchase #4	$48.34	6.516%	$51.4898	$51.49	$51.50	$51.50
Purchase #5	$189.57	3.672%	$196.531	$196.53	$196.55	$196.50
Purchase #6	$29.86	6.679%	$31.8543	$31.85	$31.85	$31.90
Purchase #7	$104.44	12.594%	$117.5932	$117.59	$117.60	$117.60
7 purchase totals =	$591.08		$643.3493	$643.35	$643.40	$643.30