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	$80.47	13.682%	$91.4799	$91.48	$91.50	$91.50
Purchase #2	$150.99	10.851%	$167.3739	$167.37	$167.35	$167.40
Purchase #3	$149.87	13.210%	$169.6678	$169.67	$169.65	$169.70
Purchase #4	$128.96	4.305%	$134.5117	$134.51	$134.50	$134.50
Purchase #5	$69.81	3.434%	$72.2073	$72.21	$72.20	$72.20
Purchase #6	$148.91	6.326%	$158.33	$158.33	$158.35	$158.30
Purchase #7	$78.41	12.779%	$88.43	$88.43	$88.45	$88.40
7 purchase totals =	$807.42		$882.0006	$882.00	$882.00	$882.00