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	$68.56	9.245%	$74.8984	$74.90	$74.90	$74.90
Purchase #2	$122.97	11.364%	$136.9443	$136.94	$136.95	$136.90
Purchase #3	$55.89	10.154%	$61.5651	$61.57	$61.55	$61.60
Purchase #4	$101.74	3.676%	$105.48	$105.48	$105.50	$105.50
Purchase #5	$240.87	7.445%	$258.8028	$258.80	$258.80	$258.80
Purchase #6	$174.38	12.435%	$196.0642	$196.06	$196.05	$196.10
Purchase #7	$23.39	9.347%	$25.5763	$25.58	$25.60	$25.60
7 purchase totals =	$787.80		$859.3311	$859.33	$859.35	$859.40