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	$231.83	10.373%	$255.8777	$255.88	$255.90	$255.90
Purchase #2	$128.31	11.114%	$142.5704	$142.57	$142.55	$142.60
Purchase #3	$90.82	11.318%	$101.099	$101.10	$101.10	$101.10
Purchase #4	$84.40	12.115%	$94.6251	$94.63	$94.65	$94.60
Purchase #5	$9.91	11.793%	$11.0787	$11.08	$11.10	$11.10
Purchase #6	$157.25	3.505%	$162.7616	$162.76	$162.75	$162.80
Purchase #7	$242.29	3.697%	$251.2475	$251.25	$251.25	$251.20
7 purchase totals =	$944.81		$1,019.2600	$1,019.27	$1,019.30	$1,019.30