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	$56.60	5.788%	$59.876	$59.88	$59.90	$59.90
Purchase #2	$239.58	7.482%	$257.5054	$257.51	$257.50	$257.50
Purchase #3	$147.66	11.499%	$164.6394	$164.64	$164.65	$164.60
Purchase #4	$49.25	3.446%	$50.9472	$50.95	$50.95	$50.90
Purchase #5	$38.53	5.808%	$40.7678	$40.77	$40.75	$40.80
Purchase #6	$95.44	11.551%	$106.4643	$106.46	$106.45	$106.50
Purchase #7	$238.72	5.365%	$251.5273	$251.53	$251.55	$251.50
7 purchase totals =	$865.78		$931.7274	$931.74	$931.75	$931.70