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	$133.41	5.378%	$140.5848	$140.58	$140.60	$140.60
Purchase #2	$165.68	10.760%	$183.5072	$183.51	$183.50	$183.50
Purchase #3	$165.98	3.849%	$172.3686	$172.37	$172.35	$172.40
Purchase #4	$111.91	3.505%	$115.8324	$115.83	$115.85	$115.80
Purchase #5	$97.32	12.462%	$109.448	$109.45	$109.45	$109.40
Purchase #6	$194.63	4.204%	$202.8122	$202.81	$202.80	$202.80
Purchase #7	$142.45	10.163%	$156.9272	$156.93	$156.95	$156.90
7 purchase totals =	$1,011.38		$1,081.4804	$1,081.48	$1,081.50	$1,081.40