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	$36.65	10.589%	$40.5309	$40.53	$40.55	$40.50
Purchase #2	$40.37	6.251%	$42.8935	$42.89	$42.90	$42.90
Purchase #3	$87.94	3.450%	$90.9739	$90.97	$90.95	$91.00
Purchase #4	$169.94	11.412%	$189.3336	$189.33	$189.35	$189.30
Purchase #5	$155.35	11.498%	$173.2121	$173.21	$173.20	$173.20
Purchase #6	$216.44	11.406%	$241.1271	$241.13	$241.15	$241.10
Purchase #7	$155.46	7.634%	$167.3278	$167.33	$167.35	$167.30
7 purchase totals =	$862.15		$945.3989	$945.39	$945.45	$945.30