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	$231.60	10.152%	$255.112	$255.11	$255.10	$255.10
Purchase #2	$164.90	3.319%	$170.373	$170.37	$170.35	$170.40
Purchase #3	$29.42	8.711%	$31.9828	$31.98	$32.00	$32.00
Purchase #4	$39.37	7.613%	$42.3672	$42.37	$42.35	$42.40
Purchase #5	$156.51	6.762%	$167.0932	$167.09	$167.10	$167.10
Purchase #6	$226.34	13.504%	$256.905	$256.91	$256.90	$256.90
Purchase #7	$45.31	11.150%	$50.3621	$50.36	$50.35	$50.40
7 purchase totals =	$893.45		$974.1953	$974.19	$974.15	$974.30