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	$103.51	3.811%	$107.4548	$107.45	$107.45	$107.50
Purchase #2	$79.66	5.312%	$83.8915	$83.89	$83.90	$83.90
Purchase #3	$12.33	4.489%	$12.8835	$12.88	$12.90	$12.90
Purchase #4	$7.97	5.851%	$8.4363	$8.44	$8.45	$8.40
Purchase #5	$171.89	7.634%	$185.0121	$185.01	$185.00	$185.00
Purchase #6	$225.87	12.328%	$253.7153	$253.72	$253.70	$253.70
Purchase #7	$205.71	8.205%	$222.5885	$222.59	$222.60	$222.60
7 purchase totals =	$806.94		$873.9820	$873.98	$874.00	$874.00