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	$50.96	3.231%	$52.6065	$52.61	$52.60	$52.60
Purchase #2	$34.76	5.695%	$36.7396	$36.74	$36.75	$36.70
Purchase #3	$19.94	3.116%	$20.5613	$20.56	$20.55	$20.60
Purchase #4	$88.79	7.212%	$95.1935	$95.19	$95.20	$95.20
Purchase #5	$39.63	12.462%	$44.5687	$44.57	$44.55	$44.60
Purchase #6	$104.95	6.325%	$111.5881	$111.59	$111.60	$111.60
Purchase #7	$178.89	3.544%	$185.2299	$185.23	$185.25	$185.20
7 purchase totals =	$517.92		$546.4876	$546.49	$546.50	$546.50