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	$94.41	12.382%	$106.0998	$106.10	$106.10	$106.10
Purchase #2	$57.69	8.514%	$62.6017	$62.60	$62.60	$62.60
Purchase #3	$46.71	10.443%	$51.5879	$51.59	$51.60	$51.60
Purchase #4	$60.33	11.138%	$67.0496	$67.05	$67.05	$67.00
Purchase #5	$94.71	9.348%	$103.5635	$103.56	$103.55	$103.60
Purchase #6	$98.53	8.810%	$107.2105	$107.21	$107.20	$107.20
Purchase #7	$173.34	10.692%	$191.8735	$191.87	$191.85	$191.90
7 purchase totals =	$625.72		$689.9865	$689.98	$689.95	$690.00