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	$33.25	4.400%	$34.713	$34.71	$34.70	$34.70
Purchase #2	$175.40	6.560%	$186.9062	$186.91	$186.90	$186.90
Purchase #3	$40.74	5.208%	$42.8617	$42.86	$42.85	$42.90
Purchase #4	$127.86	9.800%	$140.3903	$140.39	$140.40	$140.40
Purchase #5	$39.81	9.312%	$43.5171	$43.52	$43.50	$43.50
Purchase #6	$169.66	3.837%	$176.1699	$176.17	$176.15	$176.20
Purchase #7	$161.50	9.535%	$176.899	$176.90	$176.90	$176.90
7 purchase totals =	$748.22		$801.4572	$801.46	$801.40	$801.50