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	$126.80	12.386%	$142.5054	$142.51	$142.50	$142.50
Purchase #2	$159.60	12.771%	$179.9825	$179.98	$180.00	$180.00
Purchase #3	$59.73	12.873%	$67.419	$67.42	$67.40	$67.40
Purchase #4	$34.30	12.560%	$38.6081	$38.61	$38.60	$38.60
Purchase #5	$179.87	10.272%	$198.3462	$198.35	$198.35	$198.30
Purchase #6	$170.96	12.131%	$191.6992	$191.70	$191.70	$191.70
Purchase #7	$129.33	7.773%	$139.3828	$139.38	$139.40	$139.40
7 purchase totals =	$860.59		$957.9432	$957.95	$957.95	$957.90