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	$115.64	7.601%	$124.4298	$124.43	$124.45	$124.40
Purchase #2	$102.73	6.269%	$109.1701	$109.17	$109.15	$109.20
Purchase #3	$159.48	8.202%	$172.5605	$172.56	$172.55	$172.60
Purchase #4	$111.29	5.529%	$117.4432	$117.44	$117.45	$117.40
Purchase #5	$48.78	8.456%	$52.9048	$52.90	$52.90	$52.90
Purchase #6	$130.67	8.310%	$141.5287	$141.53	$141.55	$141.50
Purchase #7	$57.51	13.654%	$65.3624	$65.36	$65.35	$65.40
7 purchase totals =	$726.10		$783.3995	$783.39	$783.40	$783.40