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	$19.34	7.443%	$20.7795	$20.78	$20.80	$20.80
Purchase #2	$153.69	9.649%	$168.5195	$168.52	$168.50	$168.50
Purchase #3	$142.92	4.638%	$149.5486	$149.55	$149.55	$149.50
Purchase #4	$31.84	6.262%	$33.8338	$33.83	$33.85	$33.80
Purchase #5	$103.65	12.744%	$116.8592	$116.86	$116.85	$116.90
Purchase #6	$55.48	8.243%	$60.0532	$60.05	$60.05	$60.10
Purchase #7	$119.31	12.265%	$133.9434	$133.94	$133.95	$133.90
7 purchase totals =	$626.23		$683.5372	$683.53	$683.55	$683.50