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	$84.63	6.295%	$89.9575	$89.96	$89.95	$90.00
Purchase #2	$133.47	10.790%	$147.8714	$147.87	$147.85	$147.90
Purchase #3	$175.84	4.570%	$183.8759	$183.88	$183.90	$183.90
Purchase #4	$162.52	7.571%	$174.8244	$174.82	$174.80	$174.80
Purchase #5	$22.40	4.757%	$23.4656	$23.47	$23.45	$23.50
Purchase #6	$53.70	3.859%	$55.7723	$55.77	$55.75	$55.80
Purchase #7	$100.82	10.175%	$111.0784	$111.08	$111.10	$111.10
7 purchase totals =	$733.38		$786.8455	$786.85	$786.80	$787.00