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	$87.81	13.279%	$99.4703	$99.47	$99.45	$99.50
Purchase #2	$201.86	6.713%	$215.4109	$215.41	$215.40	$215.40
Purchase #3	$196.87	9.215%	$215.0116	$215.01	$215.00	$215.00
Purchase #4	$205.62	11.399%	$229.0586	$229.06	$229.05	$229.10
Purchase #5	$125.33	13.260%	$141.9488	$141.95	$141.95	$141.90
Purchase #6	$115.79	11.131%	$128.6786	$128.68	$128.70	$128.70
Purchase #7	$33.87	11.665%	$37.8209	$37.82	$37.80	$37.80
7 purchase totals =	$967.15		$1,067.3997	$1,067.40	$1,067.35	$1,067.40