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	$17.66	12.546%	$19.8756	$19.88	$19.90	$19.90
Purchase #2	$90.27	11.399%	$100.5599	$100.56	$100.55	$100.60
Purchase #3	$248.47	3.817%	$257.9541	$257.95	$257.95	$258.00
Purchase #4	$222.60	8.457%	$241.4253	$241.43	$241.45	$241.40
Purchase #5	$166.38	10.318%	$183.5471	$183.55	$183.55	$183.50
Purchase #6	$217.66	3.591%	$225.4762	$225.48	$225.50	$225.50
Purchase #7	$78.94	8.477%	$85.6317	$85.63	$85.65	$85.60
7 purchase totals =	$1,041.98		$1,114.4699	$1,114.48	$1,114.55	$1,114.50