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	$123.78	12.701%	$139.5013	$139.50	$139.50	$139.50
Purchase #2	$165.38	3.369%	$170.9517	$170.95	$170.95	$171.00
Purchase #3	$146.34	12.213%	$164.2125	$164.21	$164.20	$164.20
Purchase #4	$107.34	11.410%	$119.5875	$119.59	$119.60	$119.60
Purchase #5	$148.90	13.669%	$169.2531	$169.25	$169.25	$169.30
Purchase #6	$151.46	8.455%	$164.2659	$164.27	$164.25	$164.30
Purchase #7	$170.25	12.435%	$191.4206	$191.42	$191.40	$191.40
7 purchase totals =	$1,013.45		$1,119.1926	$1,119.19	$1,119.15	$1,119.30