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	$96.67	3.338%	$99.8968	$99.90	$99.90	$99.90
Purchase #2	$70.91	6.494%	$75.5149	$75.51	$75.50	$75.50
Purchase #3	$211.76	4.304%	$220.8742	$220.87	$220.85	$220.90
Purchase #4	$95.64	10.202%	$105.3972	$105.40	$105.40	$105.40
Purchase #5	$30.83	6.652%	$32.8808	$32.88	$32.90	$32.90
Purchase #6	$42.57	3.223%	$43.942	$43.94	$43.95	$43.90
Purchase #7	$97.61	7.862%	$105.2841	$105.28	$105.30	$105.30
7 purchase totals =	$645.99		$683.7900	$683.78	$683.80	$683.80