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	$179.51	6.562%	$191.2894	$191.29	$191.30	$191.30
Purchase #2	$209.99	8.317%	$227.4549	$227.45	$227.45	$227.50
Purchase #3	$109.33	9.417%	$119.6256	$119.63	$119.65	$119.60
Purchase #4	$76.41	7.845%	$82.4044	$82.40	$82.40	$82.40
Purchase #5	$41.45	5.688%	$43.8077	$43.81	$43.80	$43.80
Purchase #6	$20.77	5.413%	$21.8943	$21.89	$21.90	$21.90
Purchase #7	$72.31	3.407%	$74.7736	$74.77	$74.75	$74.80
7 purchase totals =	$709.77		$761.2499	$761.24	$761.25	$761.30