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	$136.97	11.507%	$152.7311	$152.73	$152.75	$152.70
Purchase #2	$74.85	5.270%	$78.7946	$78.79	$78.80	$78.80
Purchase #3	$16.87	5.475%	$17.7936	$17.79	$17.80	$17.80
Purchase #4	$176.78	10.816%	$195.9005	$195.90	$195.90	$195.90
Purchase #5	$24.25	13.484%	$27.5199	$27.52	$27.50	$27.50
Purchase #6	$130.66	9.339%	$142.8623	$142.86	$142.85	$142.90
Purchase #7	$237.80	13.698%	$270.3738	$270.37	$270.35	$270.40
7 purchase totals =	$798.18		$885.9758	$885.96	$885.95	$886.00