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	$108.79	5.316%	$114.5733	$114.57	$114.55	$114.60
Purchase #2	$196.86	11.154%	$218.8178	$218.82	$218.80	$218.80
Purchase #3	$63.66	10.538%	$70.3685	$70.37	$70.35	$70.40
Purchase #4	$185.73	5.226%	$195.4362	$195.44	$195.45	$195.40
Purchase #5	$84.78	7.208%	$90.8909	$90.89	$90.90	$90.90
Purchase #6	$39.35	7.687%	$42.3748	$42.37	$42.35	$42.40
Purchase #7	$179.83	4.204%	$187.3901	$187.39	$187.40	$187.40
7 purchase totals =	$859.00		$919.8516	$919.85	$919.80	$919.90