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	$48.86	4.428%	$51.0235	$51.02	$51.00	$51.00
Purchase #2	$73.74	5.184%	$77.5627	$77.56	$77.55	$77.60
Purchase #3	$39.66	13.112%	$44.8602	$44.86	$44.85	$44.90
Purchase #4	$189.53	3.659%	$196.4649	$196.46	$196.45	$196.50
Purchase #5	$211.71	9.391%	$231.5917	$231.59	$231.60	$231.60
Purchase #6	$79.77	9.398%	$87.2668	$87.27	$87.25	$87.30
Purchase #7	$177.90	12.707%	$200.5058	$200.51	$200.50	$200.50
7 purchase totals =	$821.17		$889.2756	$889.27	$889.20	$889.40