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	$90.52	11.441%	$100.8764	$100.88	$100.90	$100.90
Purchase #2	$121.91	5.655%	$128.804	$128.80	$128.80	$128.80
Purchase #3	$135.90	8.797%	$147.8551	$147.86	$147.85	$147.90
Purchase #4	$29.78	9.124%	$32.4971	$32.50	$32.50	$32.50
Purchase #5	$200.64	5.483%	$211.6411	$211.64	$211.65	$211.60
Purchase #6	$182.77	13.415%	$207.2886	$207.29	$207.30	$207.30
Purchase #7	$65.55	10.479%	$72.419	$72.42	$72.40	$72.40
7 purchase totals =	$827.07		$901.3813	$901.39	$901.40	$901.40