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	$105.71	6.778%	$112.875	$112.88	$112.90	$112.90
Purchase #2	$101.72	4.290%	$106.0838	$106.08	$106.10	$106.10
Purchase #3	$123.57	5.243%	$130.0488	$130.05	$130.05	$130.00
Purchase #4	$56.39	10.144%	$62.1102	$62.11	$62.10	$62.10
Purchase #5	$152.71	13.582%	$173.4511	$173.45	$173.45	$173.50
Purchase #6	$165.95	4.364%	$173.1921	$173.19	$173.20	$173.20
Purchase #7	$93.78	9.411%	$102.6056	$102.61	$102.60	$102.60
7 purchase totals =	$799.83		$860.3666	$860.37	$860.40	$860.40