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	$174.93	6.645%	$186.5541	$186.55	$186.55	$186.60
Purchase #2	$169.92	11.852%	$190.0589	$190.06	$190.05	$190.10
Purchase #3	$212.41	4.780%	$222.5632	$222.56	$222.55	$222.60
Purchase #4	$46.70	10.450%	$51.5802	$51.58	$51.60	$51.60
Purchase #5	$204.70	6.665%	$218.3433	$218.34	$218.35	$218.30
Purchase #6	$6.91	6.610%	$7.3668	$7.37	$7.35	$7.40
Purchase #7	$99.69	13.264%	$112.9129	$112.91	$112.90	$112.90
7 purchase totals =	$915.26		$989.3794	$989.37	$989.35	$989.50