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	$55.40	3.416%	$57.2925	$57.29	$57.30	$57.30
Purchase #2	$220.41	13.240%	$249.5923	$249.59	$249.60	$249.60
Purchase #3	$174.52	12.577%	$196.4694	$196.47	$196.45	$196.50
Purchase #4	$68.96	3.382%	$71.2922	$71.29	$71.30	$71.30
Purchase #5	$184.99	11.782%	$206.7855	$206.79	$206.80	$206.80
Purchase #6	$51.96	6.188%	$55.1753	$55.18	$55.20	$55.20
Purchase #7	$100.37	13.527%	$113.947	$113.95	$113.95	$113.90
7 purchase totals =	$856.61		$950.5542	$950.56	$950.60	$950.60