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	$113.33	12.362%	$127.3399	$127.34	$127.35	$127.30
Purchase #2	$147.83	11.426%	$164.7211	$164.72	$164.70	$164.70
Purchase #3	$138.61	12.816%	$156.3743	$156.37	$156.35	$156.40
Purchase #4	$72.61	13.106%	$82.1263	$82.13	$82.15	$82.10
Purchase #5	$123.69	4.387%	$129.1163	$129.12	$129.10	$129.10
Purchase #6	$237.39	5.423%	$250.2637	$250.26	$250.25	$250.30
Purchase #7	$27.81	11.560%	$31.0248	$31.02	$31.00	$31.00
7 purchase totals =	$861.27		$940.9664	$940.96	$940.90	$940.90