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	$223.56	10.191%	$246.343	$246.34	$246.35	$246.30
Purchase #2	$33.66	10.725%	$37.27	$37.27	$37.25	$37.30
Purchase #3	$106.66	8.356%	$115.5725	$115.57	$115.55	$115.60
Purchase #4	$39.85	5.691%	$42.1179	$42.12	$42.10	$42.10
Purchase #5	$138.55	3.242%	$143.0418	$143.04	$143.05	$143.00
Purchase #6	$32.56	4.336%	$33.9718	$33.97	$33.95	$34.00
Purchase #7	$45.42	3.857%	$47.1718	$47.17	$47.15	$47.20
7 purchase totals =	$620.26		$665.4888	$665.48	$665.40	$665.50