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	$23.69	11.823%	$26.4909	$26.49	$26.50	$26.50
Purchase #2	$109.38	3.151%	$112.8266	$112.83	$112.85	$112.80
Purchase #3	$139.48	6.692%	$148.814	$148.81	$148.80	$148.80
Purchase #4	$54.53	9.862%	$59.9077	$59.91	$59.90	$59.90
Purchase #5	$78.89	7.777%	$85.0253	$85.03	$85.05	$85.00
Purchase #6	$5.78	12.242%	$6.4876	$6.49	$6.50	$6.50
Purchase #7	$144.83	9.867%	$159.1204	$159.12	$159.10	$159.10
7 purchase totals =	$556.58		$598.6725	$598.68	$598.70	$598.60