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	$27.49	7.812%	$29.6375	$29.64	$29.65	$29.60
Purchase #2	$110.90	11.371%	$123.5104	$123.51	$123.50	$123.50
Purchase #3	$54.80	12.312%	$61.547	$61.55	$61.55	$61.50
Purchase #4	$87.89	13.221%	$99.5099	$99.51	$99.50	$99.50
Purchase #5	$205.53	9.571%	$225.2013	$225.20	$225.20	$225.20
Purchase #6	$31.33	10.843%	$34.7271	$34.73	$34.75	$34.70
Purchase #7	$246.81	5.556%	$260.5228	$260.52	$260.50	$260.50
7 purchase totals =	$764.75		$834.6560	$834.66	$834.65	$834.50