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	$119.73	6.230%	$127.1892	$127.19	$127.20	$127.20
Purchase #2	$134.48	6.179%	$142.7895	$142.79	$142.80	$142.80
Purchase #3	$159.29	10.232%	$175.5886	$175.59	$175.60	$175.60
Purchase #4	$82.35	8.699%	$89.5136	$89.51	$89.50	$89.50
Purchase #5	$27.61	6.457%	$29.3928	$29.39	$29.40	$29.40
Purchase #6	$11.50	3.193%	$11.8672	$11.87	$11.85	$11.90
Purchase #7	$81.41	6.292%	$86.5323	$86.53	$86.55	$86.50
7 purchase totals =	$616.37		$662.8732	$662.87	$662.90	$662.90