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	$25.89	5.295%	$27.2609	$27.26	$27.25	$27.30
Purchase #2	$66.63	8.614%	$72.3695	$72.37	$72.35	$72.40
Purchase #3	$243.71	11.435%	$271.5782	$271.58	$271.60	$271.60
Purchase #4	$109.41	8.753%	$118.9867	$118.99	$119.00	$119.00
Purchase #5	$120.73	9.838%	$132.6074	$132.61	$132.60	$132.60
Purchase #6	$125.73	8.604%	$136.5478	$136.55	$136.55	$136.50
Purchase #7	$41.96	3.746%	$43.5318	$43.53	$43.55	$43.50
7 purchase totals =	$734.06		$802.8823	$802.89	$802.90	$802.90