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	$38.68	4.723%	$40.5069	$40.51	$40.50	$40.50
Purchase #2	$93.51	5.306%	$98.4716	$98.47	$98.45	$98.50
Purchase #3	$160.28	6.444%	$170.6084	$170.61	$170.60	$170.60
Purchase #4	$127.71	11.527%	$142.4311	$142.43	$142.45	$142.40
Purchase #5	$127.60	13.736%	$145.1271	$145.13	$145.15	$145.10
Purchase #6	$81.54	3.708%	$84.5635	$84.56	$84.55	$84.60
Purchase #7	$170.59	5.833%	$180.5405	$180.54	$180.55	$180.50
7 purchase totals =	$799.91		$862.2491	$862.25	$862.25	$862.20