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	$36.68	8.202%	$39.6885	$39.69	$39.70	$39.70
Purchase #2	$72.44	8.188%	$78.3714	$78.37	$78.35	$78.40
Purchase #3	$172.60	8.854%	$187.882	$187.88	$187.90	$187.90
Purchase #4	$97.29	6.569%	$103.681	$103.68	$103.70	$103.70
Purchase #5	$42.90	5.402%	$45.2175	$45.22	$45.20	$45.20
Purchase #6	$19.89	8.715%	$21.6234	$21.62	$21.60	$21.60
Purchase #7	$17.46	5.504%	$18.421	$18.42	$18.40	$18.40
7 purchase totals =	$459.26		$494.8848	$494.88	$494.85	$494.90