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	$66.42	8.723%	$72.2138	$72.21	$72.20	$72.20
Purchase #2	$105.36	13.385%	$119.4624	$119.46	$119.45	$119.50
Purchase #3	$141.94	10.414%	$156.7216	$156.72	$156.70	$156.70
Purchase #4	$151.56	3.500%	$156.8646	$156.86	$156.85	$156.90
Purchase #5	$217.86	7.826%	$234.9097	$234.91	$234.90	$234.90
Purchase #6	$13.50	3.518%	$13.9749	$13.97	$13.95	$14.00
Purchase #7	$44.33	7.661%	$47.7261	$47.73	$47.75	$47.70
7 purchase totals =	$740.97		$801.8731	$801.86	$801.80	$801.90