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	$88.49	12.288%	$99.3637	$99.36	$99.35	$99.40
Purchase #2	$151.57	12.338%	$170.2707	$170.27	$170.25	$170.30
Purchase #3	$109.74	13.848%	$124.9368	$124.94	$124.95	$124.90
Purchase #4	$123.35	12.865%	$139.219	$139.22	$139.20	$139.20
Purchase #5	$69.37	5.851%	$73.4288	$73.43	$73.45	$73.40
Purchase #6	$103.71	6.407%	$110.3547	$110.35	$110.35	$110.40
Purchase #7	$71.58	9.611%	$78.4596	$78.46	$78.45	$78.50
7 purchase totals =	$717.81		$796.0333	$796.03	$796.00	$796.10