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	$86.77	4.110%	$90.3362	$90.34	$90.35	$90.30
Purchase #2	$199.97	3.125%	$206.2191	$206.22	$206.20	$206.20
Purchase #3	$19.45	4.854%	$20.3941	$20.39	$20.40	$20.40
Purchase #4	$11.68	5.190%	$12.2862	$12.29	$12.30	$12.30
Purchase #5	$79.61	3.713%	$82.5659	$82.57	$82.55	$82.60
Purchase #6	$245.95	5.263%	$258.8943	$258.89	$258.90	$258.90
Purchase #7	$249.39	13.307%	$282.5763	$282.58	$282.60	$282.60
7 purchase totals =	$892.82		$953.2721	$953.28	$953.30	$953.30