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	$160.91	6.197%	$170.8816	$170.88	$170.90	$170.90
Purchase #2	$77.56	6.816%	$82.8465	$82.85	$82.85	$82.80
Purchase #3	$54.37	9.535%	$59.5542	$59.55	$59.55	$59.60
Purchase #4	$224.79	13.724%	$255.6402	$255.64	$255.65	$255.60
Purchase #5	$105.84	11.561%	$118.0762	$118.08	$118.10	$118.10
Purchase #6	$196.87	9.762%	$216.0884	$216.09	$216.10	$216.10
Purchase #7	$5.71	6.839%	$6.1005	$6.10	$6.10	$6.10
7 purchase totals =	$826.05		$909.1876	$909.19	$909.25	$909.20