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	$226.98	9.482%	$248.5022	$248.50	$248.50	$248.50
Purchase #2	$237.45	11.190%	$264.0207	$264.02	$264.00	$264.00
Purchase #3	$143.32	13.418%	$162.5507	$162.55	$162.55	$162.60
Purchase #4	$176.68	5.440%	$186.2914	$186.29	$186.30	$186.30
Purchase #5	$127.25	11.312%	$141.6445	$141.64	$141.65	$141.60
Purchase #6	$71.36	7.714%	$76.8647	$76.86	$76.85	$76.90
Purchase #7	$127.30	13.134%	$144.0196	$144.02	$144.00	$144.00
7 purchase totals =	$1,110.34		$1,223.8938	$1,223.88	$1,223.85	$1,223.90