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	$159.88	4.710%	$167.4103	$167.41	$167.40	$167.40
Purchase #2	$205.47	7.724%	$221.3405	$221.34	$221.35	$221.30
Purchase #3	$125.91	10.857%	$139.58	$139.58	$139.60	$139.60
Purchase #4	$178.35	12.166%	$200.0481	$200.05	$200.05	$200.00
Purchase #5	$82.86	12.105%	$92.8902	$92.89	$92.90	$92.90
Purchase #6	$141.71	9.284%	$154.8664	$154.87	$154.85	$154.90
Purchase #7	$229.98	3.636%	$238.3421	$238.34	$238.35	$238.30
7 purchase totals =	$1,124.16		$1,214.4776	$1,214.48	$1,214.50	$1,214.40