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	$88.62	8.208%	$95.8939	$95.89	$95.90	$95.90
Purchase #2	$46.30	3.300%	$47.8279	$47.83	$47.85	$47.80
Purchase #3	$75.60	8.315%	$81.8861	$81.89	$81.90	$81.90
Purchase #4	$70.64	3.110%	$72.8369	$72.84	$72.85	$72.80
Purchase #5	$144.29	7.549%	$155.1825	$155.18	$155.20	$155.20
Purchase #6	$169.89	11.634%	$189.655	$189.66	$189.65	$189.70
Purchase #7	$186.75	5.341%	$196.7243	$196.72	$196.70	$196.70
7 purchase totals =	$782.09		$840.0066	$840.01	$840.05	$840.00