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	$47.88	5.336%	$50.4349	$50.43	$50.45	$50.40
Purchase #2	$233.92	13.530%	$265.5694	$265.57	$265.55	$265.60
Purchase #3	$38.56	11.818%	$43.117	$43.12	$43.10	$43.10
Purchase #4	$19.41	12.214%	$21.7807	$21.78	$21.80	$21.80
Purchase #5	$193.29	13.559%	$219.4982	$219.50	$219.50	$219.50
Purchase #6	$9.30	12.650%	$10.4765	$10.48	$10.50	$10.50
Purchase #7	$238.97	13.650%	$271.5894	$271.59	$271.60	$271.60
7 purchase totals =	$781.33		$882.4661	$882.47	$882.50	$882.50