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	$81.62	12.555%	$91.8674	$91.87	$91.85	$91.90
Purchase #2	$101.64	8.803%	$110.5874	$110.59	$110.60	$110.60
Purchase #3	$10.32	10.485%	$11.4021	$11.40	$11.40	$11.40
Purchase #4	$212.72	10.710%	$235.5023	$235.50	$235.50	$235.50
Purchase #5	$19.50	12.363%	$21.9108	$21.91	$21.90	$21.90
Purchase #6	$210.46	9.588%	$230.6389	$230.64	$230.65	$230.60
Purchase #7	$80.33	12.726%	$90.5528	$90.55	$90.55	$90.60
7 purchase totals =	$716.59		$792.4617	$792.46	$792.45	$792.50