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	$125.90	3.338%	$130.1025	$130.10	$130.10	$130.10
Purchase #2	$38.65	3.294%	$39.9231	$39.92	$39.90	$39.90
Purchase #3	$40.83	6.280%	$43.3941	$43.39	$43.40	$43.40
Purchase #4	$19.64	11.772%	$21.952	$21.95	$21.95	$22.00
Purchase #5	$84.85	12.235%	$95.2314	$95.23	$95.25	$95.20
Purchase #6	$163.29	3.130%	$168.401	$168.40	$168.40	$168.40
Purchase #7	$133.29	13.150%	$150.8176	$150.82	$150.80	$150.80
7 purchase totals =	$606.45		$649.8217	$649.81	$649.80	$649.80