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	$174.25	3.611%	$180.5422	$180.54	$180.55	$180.50
Purchase #2	$32.53	6.334%	$34.5905	$34.59	$34.60	$34.60
Purchase #3	$29.33	10.778%	$32.4912	$32.49	$32.50	$32.50
Purchase #4	$42.29	13.341%	$47.9319	$47.93	$47.95	$47.90
Purchase #5	$67.27	5.716%	$71.1152	$71.12	$71.10	$71.10
Purchase #6	$112.95	8.771%	$122.8568	$122.86	$122.85	$122.90
Purchase #7	$82.26	3.855%	$85.4311	$85.43	$85.45	$85.40
7 purchase totals =	$540.88		$574.9589	$574.96	$575.00	$574.90