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	$117.80	11.327%	$131.1432	$131.14	$131.15	$131.10
Purchase #2	$159.89	5.616%	$168.8694	$168.87	$168.85	$168.90
Purchase #3	$148.72	10.415%	$164.2092	$164.21	$164.20	$164.20
Purchase #4	$144.34	12.220%	$161.9783	$161.98	$162.00	$162.00
Purchase #5	$65.28	11.463%	$72.763	$72.76	$72.75	$72.80
Purchase #6	$13.65	12.437%	$15.3477	$15.35	$15.35	$15.30
Purchase #7	$228.81	13.212%	$259.0404	$259.04	$259.05	$259.00
7 purchase totals =	$878.49		$973.3512	$973.35	$973.35	$973.30