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	$170.36	11.354%	$189.7027	$189.70	$189.70	$189.70
Purchase #2	$59.87	8.627%	$65.035	$65.04	$65.05	$65.00
Purchase #3	$154.30	6.329%	$164.0656	$164.07	$164.05	$164.10
Purchase #4	$63.27	13.512%	$71.819	$71.82	$71.80	$71.80
Purchase #5	$127.63	8.736%	$138.7798	$138.78	$138.80	$138.80
Purchase #6	$24.88	10.873%	$27.5852	$27.59	$27.60	$27.60
Purchase #7	$168.38	10.146%	$185.4638	$185.46	$185.45	$185.50
7 purchase totals =	$768.69		$842.4511	$842.46	$842.45	$842.50