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	$159.76	11.787%	$178.5909	$178.59	$178.60	$178.60
Purchase #2	$84.81	6.753%	$90.5372	$90.54	$90.55	$90.50
Purchase #3	$159.74	7.304%	$171.4074	$171.41	$171.40	$171.40
Purchase #4	$94.99	11.509%	$105.9224	$105.92	$105.90	$105.90
Purchase #5	$220.75	6.137%	$234.2974	$234.30	$234.30	$234.30
Purchase #6	$151.85	11.279%	$168.9772	$168.98	$169.00	$169.00
Purchase #7	$91.60	6.193%	$97.2728	$97.27	$97.25	$97.30
7 purchase totals =	$963.50		$1,047.0053	$1,047.01	$1,047.00	$1,047.00