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	$71.81	9.829%	$78.8682	$78.87	$78.85	$78.90
Purchase #2	$36.81	5.792%	$38.942	$38.94	$38.95	$38.90
Purchase #3	$20.46	3.562%	$21.1888	$21.19	$21.20	$21.20
Purchase #4	$154.63	4.440%	$161.4956	$161.50	$161.50	$161.50
Purchase #5	$124.71	5.455%	$131.5129	$131.51	$131.50	$131.50
Purchase #6	$221.80	10.809%	$245.7744	$245.77	$245.75	$245.80
Purchase #7	$53.75	6.633%	$57.3152	$57.32	$57.30	$57.30
7 purchase totals =	$683.97		$735.0971	$735.10	$735.05	$735.10