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	$35.69	5.377%	$37.6091	$37.61	$37.60	$37.60
Purchase #2	$82.67	9.426%	$90.4625	$90.46	$90.45	$90.50
Purchase #3	$163.38	3.370%	$168.8859	$168.89	$168.90	$168.90
Purchase #4	$158.86	9.154%	$173.402	$173.40	$173.40	$173.40
Purchase #5	$82.45	10.766%	$91.3266	$91.33	$91.35	$91.30
Purchase #6	$115.75	6.792%	$123.6117	$123.61	$123.60	$123.60
Purchase #7	$179.29	11.302%	$199.5534	$199.55	$199.55	$199.60
7 purchase totals =	$818.09		$884.8512	$884.85	$884.85	$884.90