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	$152.48	8.140%	$164.8919	$164.89	$164.90	$164.90
Purchase #2	$191.78	6.252%	$203.7701	$203.77	$203.75	$203.80
Purchase #3	$128.59	8.121%	$139.0328	$139.03	$139.05	$139.00
Purchase #4	$81.93	4.430%	$85.5595	$85.56	$85.55	$85.60
Purchase #5	$165.60	4.786%	$173.5256	$173.53	$173.55	$173.50
Purchase #6	$124.70	6.254%	$132.4987	$132.50	$132.50	$132.50
Purchase #7	$48.39	12.825%	$54.596	$54.60	$54.60	$54.60
7 purchase totals =	$893.47		$953.8746	$953.88	$953.90	$953.90