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	$80.80	13.275%	$91.5262	$91.53	$91.55	$91.50
Purchase #2	$222.57	3.257%	$229.8191	$229.82	$229.80	$229.80
Purchase #3	$158.64	4.551%	$165.8597	$165.86	$165.85	$165.90
Purchase #4	$169.25	12.679%	$190.7092	$190.71	$190.70	$190.70
Purchase #5	$182.57	12.584%	$205.5446	$205.54	$205.55	$205.50
Purchase #6	$155.39	8.547%	$168.6712	$168.67	$168.65	$168.70
Purchase #7	$249.98	9.597%	$273.9706	$273.97	$273.95	$274.00
7 purchase totals =	$1,219.20		$1,326.1006	$1,326.10	$1,326.05	$1,326.10