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	$82.88	13.269%	$93.8773	$93.88	$93.90	$93.90
Purchase #2	$220.63	13.507%	$250.4305	$250.43	$250.45	$250.40
Purchase #3	$123.94	11.822%	$138.5922	$138.59	$138.60	$138.60
Purchase #4	$215.46	4.160%	$224.4231	$224.42	$224.40	$224.40
Purchase #5	$25.81	8.139%	$27.9107	$27.91	$27.90	$27.90
Purchase #6	$147.37	7.614%	$158.5908	$158.59	$158.60	$158.60
Purchase #7	$158.37	8.732%	$172.1989	$172.20	$172.20	$172.20
7 purchase totals =	$974.46		$1,066.0235	$1,066.02	$1,066.05	$1,066.00