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	$65.66	3.195%	$67.7578	$67.76	$67.75	$67.80
Purchase #2	$150.53	13.531%	$170.8982	$170.90	$170.90	$170.90
Purchase #3	$31.80	12.700%	$35.8386	$35.84	$35.85	$35.80
Purchase #4	$82.38	8.758%	$89.5948	$89.59	$89.60	$89.60
Purchase #5	$22.71	4.719%	$23.7817	$23.78	$23.80	$23.80
Purchase #6	$54.36	4.700%	$56.9149	$56.91	$56.90	$56.90
Purchase #7	$100.99	11.726%	$112.8321	$112.83	$112.85	$112.80
7 purchase totals =	$508.43		$557.6181	$557.61	$557.65	$557.60