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	$52.41	8.582%	$56.9078	$56.91	$56.90	$56.90
Purchase #2	$246.88	10.821%	$273.5949	$273.59	$273.60	$273.60
Purchase #3	$62.76	6.524%	$66.8545	$66.85	$66.85	$66.90
Purchase #4	$34.98	9.254%	$38.217	$38.22	$38.20	$38.20
Purchase #5	$221.39	8.796%	$240.8635	$240.86	$240.85	$240.90
Purchase #6	$113.62	8.282%	$123.03	$123.03	$123.05	$123.00
Purchase #7	$175.74	10.403%	$194.0222	$194.02	$194.00	$194.00
7 purchase totals =	$907.78		$993.4899	$993.48	$993.45	$993.50