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	$148.59	6.601%	$158.3984	$158.40	$158.40	$158.40
Purchase #2	$52.49	6.372%	$55.8347	$55.83	$55.85	$55.80
Purchase #3	$199.72	11.507%	$222.7018	$222.70	$222.70	$222.70
Purchase #4	$154.65	6.457%	$164.6358	$164.64	$164.65	$164.60
Purchase #5	$246.65	4.160%	$256.9106	$256.91	$256.90	$256.90
Purchase #6	$191.48	10.716%	$211.999	$212.00	$212.00	$212.00
Purchase #7	$5.87	3.538%	$6.0777	$6.08	$6.10	$6.10
7 purchase totals =	$999.45		$1,076.5580	$1,076.56	$1,076.60	$1,076.50