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	$167.95	13.437%	$190.5174	$190.52	$190.50	$190.50
Purchase #2	$99.72	3.369%	$103.0796	$103.08	$103.10	$103.10
Purchase #3	$39.75	7.174%	$42.6017	$42.60	$42.60	$42.60
Purchase #4	$227.94	4.814%	$238.913	$238.91	$238.90	$238.90
Purchase #5	$171.37	10.459%	$189.2936	$189.29	$189.30	$189.30
Purchase #6	$107.93	4.738%	$113.0437	$113.04	$113.05	$113.00
Purchase #7	$9.62	10.540%	$10.6339	$10.63	$10.65	$10.60
7 purchase totals =	$824.28		$888.0829	$888.07	$888.10	$888.00