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	$69.71	12.579%	$78.4788	$78.48	$78.50	$78.50
Purchase #2	$222.65	6.640%	$237.434	$237.43	$237.45	$237.40
Purchase #3	$77.25	11.817%	$86.3786	$86.38	$86.40	$86.40
Purchase #4	$115.77	7.410%	$124.3486	$124.35	$124.35	$124.30
Purchase #5	$182.83	8.628%	$198.6046	$198.60	$198.60	$198.60
Purchase #6	$144.54	3.404%	$149.4601	$149.46	$149.45	$149.50
Purchase #7	$76.34	5.500%	$80.5387	$80.54	$80.55	$80.50
7 purchase totals =	$889.09		$955.2434	$955.24	$955.30	$955.20