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	$28.26	12.792%	$31.875	$31.88	$31.90	$31.90
Purchase #2	$158.91	5.161%	$167.1113	$167.11	$167.10	$167.10
Purchase #3	$177.52	7.123%	$190.1647	$190.16	$190.15	$190.20
Purchase #4	$219.98	9.425%	$240.7131	$240.71	$240.70	$240.70
Purchase #5	$62.72	10.563%	$69.3451	$69.35	$69.35	$69.30
Purchase #6	$245.97	7.116%	$263.4732	$263.47	$263.45	$263.50
Purchase #7	$111.42	6.844%	$119.0456	$119.05	$119.05	$119.00
7 purchase totals =	$1,004.78		$1,081.7280	$1,081.73	$1,081.70	$1,081.70