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	$92.35	9.792%	$101.3929	$101.39	$101.40	$101.40
Purchase #2	$120.98	5.328%	$127.4258	$127.43	$127.45	$127.40
Purchase #3	$37.87	6.572%	$40.3588	$40.36	$40.35	$40.40
Purchase #4	$78.29	4.860%	$82.0949	$82.09	$82.10	$82.10
Purchase #5	$7.90	5.661%	$8.3472	$8.35	$8.35	$8.30
Purchase #6	$124.78	12.407%	$140.2615	$140.26	$140.25	$140.30
Purchase #7	$27.52	9.717%	$30.1941	$30.19	$30.20	$30.20
7 purchase totals =	$489.69		$530.0752	$530.07	$530.10	$530.10