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	$89.44	7.401%	$96.0595	$96.06	$96.05	$96.10
Purchase #2	$31.25	9.853%	$34.3291	$34.33	$34.35	$34.30
Purchase #3	$65.45	9.467%	$71.6462	$71.65	$71.65	$71.60
Purchase #4	$145.55	11.296%	$161.9913	$161.99	$162.00	$162.00
Purchase #5	$110.43	12.849%	$124.6192	$124.62	$124.60	$124.60
Purchase #6	$37.35	8.462%	$40.5106	$40.51	$40.50	$40.50
Purchase #7	$126.88	9.284%	$138.6595	$138.66	$138.65	$138.70
7 purchase totals =	$606.35		$667.8154	$667.82	$667.80	$667.80