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	$115.71	11.268%	$128.7482	$128.75	$128.75	$128.70
Purchase #2	$117.62	5.134%	$123.6586	$123.66	$123.65	$123.70
Purchase #3	$241.53	3.311%	$249.5271	$249.53	$249.55	$249.50
Purchase #4	$167.90	4.570%	$175.573	$175.57	$175.55	$175.60
Purchase #5	$62.51	4.480%	$65.3104	$65.31	$65.30	$65.30
Purchase #6	$80.47	4.317%	$83.9439	$83.94	$83.95	$83.90
Purchase #7	$48.72	6.200%	$51.7406	$51.74	$51.75	$51.70
7 purchase totals =	$834.46		$878.5018	$878.50	$878.50	$878.40