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	$68.30	4.633%	$71.4643	$71.46	$71.45	$71.50
Purchase #2	$108.92	5.546%	$114.9607	$114.96	$114.95	$115.00
Purchase #3	$182.80	4.230%	$190.5324	$190.53	$190.55	$190.50
Purchase #4	$32.48	3.312%	$33.5557	$33.56	$33.55	$33.60
Purchase #5	$7.29	6.387%	$7.7556	$7.76	$7.75	$7.80
Purchase #6	$144.95	7.265%	$155.4806	$155.48	$155.50	$155.50
Purchase #7	$249.48	6.227%	$265.0151	$265.02	$265.00	$265.00
7 purchase totals =	$794.22		$838.7644	$838.77	$838.75	$838.90